MineOS is a GUI based operating system for the OpenComputers Minecraft mod. It has extensive customisation abilities as well as an app market to publish your creations among the OS community. For developers there is wonderful illustrated wiki with lots of code examples. List of main features:
Multitasking
Double buffered graphical user interface
Language packs and software localization
Multiple user profiles with password authentication
Own EEPROM firmware with boot volume choose/format/rename features and Internet Recovery mode
File sharing over the local n