The inventory features: 
Drag and drop. 
Cursors. 
Warning messages. 
Merchants with tabs, including buy-back. 
Crafting system with tabs. 
Unidentified items. 
Stackable items. 
Custom logic for dual wield, dual wielding two-handed weapons, and equipping of a two-handed weapon + a shield. 
Tooltips. 
Custom editor for creating and managing items. 
Custom editor for managing items sold by merchants.