Square One Lite does not allow you to press Option-Tab to switch between running programs. The full version does. You can't launch or switch to Square One Lite by pressing a Hot Key. Square One Lite does not have built-in commands to sort palette items, rebuild a palette's icons, or validate a palette. Lite palettes are a fixed, gray color.
Palettes can be any color in the full version.
Square One Lite does not support AppleScript. The full version does. Square One Lite does not support paged palettes. The full version does. Square One Lite does not feature spring-loaded folders.