from hyperhacker:

Luna is a completely customizable PSP shell designed to replace the XMB. It is fully themeable using Lua scripts, so skins can do just about anything - 3D effects, sounds, custom menus, you name it - without any risky or difficult firmware hacking. The skin API documentation is included, so anyone can easily make their own skins. Not a programmer? Not a problem; Lua scripting is easy, and the included skins are simple to modify or use as a base.

Bonus feature: The contents of notes.txt are displayed by pressing L, providing quick access to information such as a schedule or list of phone numbers.