diff --git a/assets/toolkit/appicon/toolkitIcon.png b/assets/toolkit/appicon/toolkitIcon.png
new file mode 100644
index 0000000..cf4932c
Binary files /dev/null and b/assets/toolkit/appicon/toolkitIcon.png differ
diff --git a/electron/index.html b/electron/index.html
index 17da275..f20118b 100644
--- a/electron/index.html
+++ b/electron/index.html
@@ -8,23 +8,86 @@
 
 <body>
     <div class="main-container">
-        <aside class="sidebar">
-            <div class="sidebar-header">
-                <h3>4DSTAR</h3>
+        <!-- Primary Category Sidebar (Tier 1) -->
+        <aside class="primary-sidebar" id="primary-sidebar">
+            <div class="primary-sidebar-header">
+                <div class="brand-icon">
+                    <div class="star-icon">✦</div>
+                    <div class="brand-text">4D</div>
+                    <h3 class="app-title">STAR</h3>
+                </div>
             </div>
-            <nav class="sidebar-nav">
-                <button id="open-bundle-btn" class="nav-button active">Open Bundle</button>
-                <button id="create-bundle-btn" class="nav-button">Create Bundle</button>
+            <nav class="category-nav">
+                <div class="category-item active" data-category="libplugin" title="libplugin">
+                    <div class="category-icon" style="background-color: #3b82f6;">LP</div>
+                    <span class="category-label">libplugin</span>
+                </div>
+                <div class="category-item" data-category="libconstants" title="libconstants">
+                    <div class="category-icon" style="background-color: #10b981;">LC</div>
+                    <span class="category-label">libconstants</span>
+                </div>
+                <div class="category-item" data-category="opat" title="OPAT Core">
+                    <div class="category-icon" style="background-color: #f59e0b;">OC</div>
+                    <span class="category-label">OPAT Core</span>
+                </div>
+                <div class="category-item" data-category="serif" title="SERiF Libraries">
+                    <div class="category-icon" style="background-color: #ef4444;">SL</div>
+                    <span class="category-label">SERiF Libraries</span>
+                </div>
             </nav>
-            <div class="sidebar-footer">
-                <p>v1.0.0</p>
+            <div class="primary-sidebar-footer">
+                <div class="version-info">v1.0.0</div>
                 <button id="info-btn" class="info-button" title="About 4DSTAR">
                     <span class="info-icon">ℹ️</span>
-                    Info
+                    <span class="info-label">Info</span>
                 </button>
             </div>
         </aside>
 
+        <!-- Secondary Content Sidebar (Tier 2) -->
+        <aside class="secondary-sidebar" id="secondary-sidebar">
+            <!-- libplugin content (existing sidebar content) -->
+            <div class="sidebar-content" data-category="libplugin">
+                <div class="sidebar-header">
+                    <h3>Bundle Manager</h3>
+                </div>
+                <nav class="sidebar-nav">
+                    <button id="open-bundle-btn" class="nav-button active">Open Bundle</button>
+                    <button id="create-bundle-btn" class="nav-button">Create Bundle</button>
+                </nav>
+            </div>
+
+            <!-- libconstants content (empty for now) -->
+            <div class="sidebar-content hidden" data-category="libconstants">
+                <div class="sidebar-header">
+                    <h3>Constants</h3>
+                </div>
+                <div class="empty-state">
+                    <p>Constants tools coming soon...</p>
+                </div>
+            </div>
+
+            <!-- OPAT Core content (empty for now) -->
+            <div class="sidebar-content hidden" data-category="opat">
+                <div class="sidebar-header">
+                    <h3>OPAT Core</h3>
+                </div>
+                <div class="empty-state">
+                    <p>OPAT tools coming soon...</p>
+                </div>
+            </div>
+
+            <!-- SERiF Libraries content (empty for now) -->
+            <div class="sidebar-content hidden" data-category="serif">
+                <div class="sidebar-header">
+                    <h3>SERiF Libraries</h3>
+                </div>
+                <div class="empty-state">
+                    <p>SERiF tools coming soon...</p>
+                </div>
+            </div>
+        </aside>
+
         <main class="content-area">
             <div id="welcome-screen">
                 <h1>Welcome to 4DSTAR Bundle Manager</h1>
diff --git a/electron/main.js b/electron/main.js
index 0d8303f..e384711 100644
--- a/electron/main.js
+++ b/electron/main.js
@@ -16,6 +16,7 @@ const createWindow = () => {
   mainWindow = new BrowserWindow({
     width: 1200,
     height: 800,
+    icon: path.join(__dirname, 'toolkitIcon.png'),
     webPreferences: {
       nodeIntegration: true,
       contextIsolation: false,
diff --git a/electron/renderer.js b/electron/renderer.js
index 96bf366..b18b943 100644
--- a/electron/renderer.js
+++ b/electron/renderer.js
@@ -258,10 +258,63 @@ function setupEventListeners() {
   // GitHub link functionality
   githubLink.addEventListener('click', (e) => {
     e.preventDefault();
+    // You can update this URL to the actual GitHub repository
     const { ipcRenderer } = require('electron');
     ipcRenderer.invoke('open-external', 'https://github.com/tboudreaux/4DSTAR');
   });
 
+  // Two-Tiered Sidebar functionality
+  const categoryItems = document.querySelectorAll('.category-item');
+  const sidebarContents = document.querySelectorAll('.sidebar-content');
+
+  // Category switching functionality
+  categoryItems.forEach(categoryItem => {
+    categoryItem.addEventListener('click', () => {
+      const selectedCategory = categoryItem.getAttribute('data-category');
+      
+      // Remove active class from all category items
+      categoryItems.forEach(item => item.classList.remove('active'));
+      
+      // Add active class to clicked category
+      categoryItem.classList.add('active');
+      
+      // Hide all sidebar contents
+      sidebarContents.forEach(content => content.classList.add('hidden'));
+      
+      // Show selected category content
+      const selectedContent = document.querySelector(`.sidebar-content[data-category="${selectedCategory}"]`);
+      if (selectedContent) {
+        selectedContent.classList.remove('hidden');
+      }
+      
+      // Update welcome screen title based on selected category
+      updateWelcomeScreen(selectedCategory);
+    });
+  });
+
+  // Update welcome screen based on selected category
+  function updateWelcomeScreen(category) {
+    const welcomeTitle = document.querySelector('#welcome-screen h1');
+    const welcomeMessage = document.querySelector('#welcome-screen p');
+    
+    const categoryTitles = {
+      'libplugin': 'Welcome to 4DSTAR Bundle Manager',
+      'libconstants': 'Welcome to 4DSTAR Constants',
+      'opat': 'Welcome to OPAT Core',
+      'serif': 'Welcome to SERiF Libraries'
+    };
+    
+    const categoryMessages = {
+      'libplugin': 'Open or create a bundle to get started.',
+      'libconstants': 'Constants tools coming soon...',
+      'opat': 'OPAT tools coming soon...',
+      'serif': 'SERiF tools coming soon...'
+    };
+    
+    if (welcomeTitle) welcomeTitle.textContent = categoryTitles[category] || 'Welcome to 4DSTAR';
+    if (welcomeMessage) welcomeMessage.textContent = categoryMessages[category] || 'Select a category to get started.';
+  }
+
   // Old modal code removed - now using tab-based interface
 
   // Create modern table-based interface for fillable targets
diff --git a/electron/styles.css b/electron/styles.css
index 2f37c03..2e44398 100644
--- a/electron/styles.css
+++ b/electron/styles.css
@@ -49,69 +49,241 @@ body {
   height: 100vh;
 }
 
-.sidebar {
-  width: var(--sidebar-width);
+/* Two-Tiered Sidebar System */
+
+/* Primary Sidebar (Tier 1) - Category Bar */
+.primary-sidebar {
+  width: 60px;
   background-color: var(--sidebar-bg);
   border-right: 1px solid var(--border-color);
   display: flex;
   flex-direction: column;
   flex-shrink: 0;
-  transition: background-color 0.2s;
+  transition: width 0.3s ease, background-color 0.2s;
+  overflow: hidden;
+  z-index: 100;
 }
 
-.sidebar-header {
+.primary-sidebar:hover {
+  width: 200px;
+}
+
+.primary-sidebar-header {
   padding: 20px;
   border-bottom: 1px solid var(--border-color);
   text-align: center;
+  white-space: nowrap;
+  background: linear-gradient(135deg, rgba(59, 130, 246, 0.05) 0%, rgba(147, 197, 253, 0.02) 100%);
+}
+
+.brand-icon {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 6px;
+  position: relative;
+}
+
+/* Ensure proper centering in collapsed state */
+.primary-sidebar:not(:hover) .brand-icon {
+  justify-content: center;
+}
+
+.primary-sidebar:not(:hover) .app-title {
+  position: absolute;
+  visibility: hidden;
+}
+
+.star-icon {
+  font-size: 18px;
+  color: #3b82f6;
+  opacity: 0.9;
+}
+
+.brand-text {
+  font-size: 16px;
+  font-weight: 700;
+  color: #1f2937;
+  letter-spacing: 1px;
+}
+
+.app-title {
+  font-size: 16px;
+  font-weight: 700;
+  color: #1f2937;
+  letter-spacing: 1px;
+  opacity: 0;
+  transition: opacity 0.3s ease;
+  margin: 0;
+}
+
+.primary-sidebar:hover .app-title {
+  opacity: 1;
+}
+
+.category-nav {
+  padding: 15px 0;
+  flex-grow: 1;
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+
+.category-item {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  padding: 12px 16px;
+  cursor: pointer;
+  transition: all 0.2s ease;
+  white-space: nowrap;
+  margin: 0;
+  position: relative;
+}
+
+.category-item:hover {
+  background-color: var(--hover-color);
+}
+
+.category-item.active {
+  background-color: rgba(59, 130, 246, 0.1);
+  border-left: 3px solid var(--primary-color);
+  padding-left: 13px;
+}
+
+.category-icon {
+  width: 36px;
+  height: 36px;
+  border-radius: 8px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  color: white;
+  font-weight: 600;
+  font-size: 14px;
+  flex-shrink: 0;
+}
+
+.category-label {
+  font-size: 0.9rem;
+  font-weight: 500;
+  opacity: 0;
+  transition: opacity 0.3s ease;
+}
+
+.primary-sidebar:hover .category-label {
+  opacity: 1;
+}
+
+.primary-sidebar-footer {
+  padding: 12px 16px 16px 16px;
+  border-top: 1px solid var(--border-color);
+  display: flex;
+  flex-direction: row;
+  align-items: center;
+  justify-content: space-between;
+  min-height: 40px;
+}
+
+.version-info {
+  font-size: 0.8rem;
+  color: var(--text-light);
+  opacity: 0;
+  transition: opacity 0.3s ease;
+}
+
+.primary-sidebar:hover .version-info {
+  opacity: 1;
+}
+
+/* Secondary Sidebar (Tier 2) - Content Sidebar */
+.secondary-sidebar {
+  width: var(--sidebar-width);
+  background-color: #fafbfc;
+  border-right: 1px solid #e5e7eb;
+  display: flex;
+  flex-direction: column;
+  flex-shrink: 0;
+  transition: background-color 0.2s;
+  box-shadow: inset -1px 0 0 rgba(0, 0, 0, 0.05);
+}
+
+.sidebar-content {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.sidebar-content.hidden {
+  display: none;
+}
+
+.sidebar-header {
+  padding: 24px 24px 20px 24px;
+  border-bottom: 1px solid #e5e7eb;
+  text-align: center;
+  background: linear-gradient(135deg, rgba(59, 130, 246, 0.02) 0%, rgba(147, 197, 253, 0.01) 100%);
 }
 
 .sidebar-header h3 {
-  font-size: 1.2rem;
-  font-weight: 600;
+  font-size: 1.3rem;
+  font-weight: 700;
+  color: #1f2937;
+  margin: 0;
+  letter-spacing: -0.025em;
 }
 
 .sidebar-nav {
-  padding: 15px 10px;
+  padding: 24px 20px;
   flex-grow: 1;
 }
 
 .nav-button {
   display: block;
   width: 100%;
-  padding: 12px 15px;
+  padding: 14px 20px;
   margin-bottom: 8px;
-  border: none;
-  border-radius: 6px;
-  background-color: transparent;
-  color: var(--text-color);
-  font-size: 0.95rem;
+  background: white;
+  border: 1px solid #e5e7eb;
   text-align: left;
   cursor: pointer;
-  transition: background-color 0.2s, color 0.2s;
+  border-radius: 10px;
+  transition: all 0.2s ease;
+  font-size: 0.95rem;
+  font-weight: 500;
+  color: #374151;
+  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
 }
 
 .nav-button:hover {
-  background-color: var(--primary-color);
-  color: white;
+  background-color: #f8fafc;
+  border-color: #d1d5db;
+  transform: translateY(-1px);
+  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
 }
 
 .nav-button.active {
-  background-color: var(--primary-color);
+  background: linear-gradient(135deg, #3b82f6 0%, #2563eb 100%);
+  border-color: #2563eb;
   color: white;
   font-weight: 600;
+  box-shadow: 0 4px 12px rgba(59, 130, 246, 0.3);
 }
 
-.sidebar-footer {
-  padding: 12px 16px 16px 16px;
-  font-size: 0.8rem;
-  color: var(--text-light);
-  display: flex;
-  flex-direction: row;
-  align-items: center;
-  justify-content: space-between;
+.nav-button.active:hover {
+  transform: translateY(-1px);
+  box-shadow: 0 6px 16px rgba(59, 130, 246, 0.4);
 }
 
-/* Info Button in Sidebar */
+.empty-state {
+  padding: 60px 24px;
+  text-align: center;
+  color: #9ca3af;
+  font-style: italic;
+  font-size: 0.95rem;
+}
+
+/* Info Button Updates */
 .info-button {
   display: flex;
   align-items: center;
@@ -137,6 +309,15 @@ body {
   font-size: 14px;
 }
 
+.info-label {
+  opacity: 0;
+  transition: opacity 0.3s ease;
+}
+
+.primary-sidebar:hover .info-label {
+  opacity: 1;
+}
+
 /* Content Area */
 .content-area {
   flex-grow: 1;
diff --git a/electron/toolkitIcon.png b/electron/toolkitIcon.png
new file mode 100644
index 0000000..cf4932c
Binary files /dev/null and b/electron/toolkitIcon.png differ
