A homebrew BIOS is Xecuter 4976.02 or EvoX D.6.
Its what enables you to read unsigned code, Backups, Imports etc. It is installed on your modchip eeprom. It can be upgraded if the modchip supports the upgrade feature.
IGR allows you perform an In Game Reset . . . i.e. return to the dashboard whilst a game is in progress.
CVS is an intermdiate release of XBMP that contains new features, bug fixes etc.
Relax is a Win32 based program used to stream media to the XBMP. An example being your pictures, mp3, movies reside on a PC and XBMP accesses them via a network connection.