PSP/Custom Firmware History

6.xx

 * PRO CFW - Unlike the other custom firmware, PRO CFW actively supports three firmware versions in every release, since some of the older ones
 * 6.61 PRO - Uses the latest official firmware.
 * 6.60 PRO
 * 6.39 PRO
 * 6.35 PRO
 * 6.20 PRO - Retained for 6.20 permapatch ability.


 * neur0n's Minimal Edition
 * 6.61 (L)ME - First real Custom Firmware (CFW) for the latest official firmware.
 * 6.60 ME - A Permanent CFW, using cIPL.
 * 6.60 LME - A Temporary CFW for all PSPs.


 * Total Noob's Homebrew Enablers
 * 6.39 TN - Updated for the new firmware.
 * 6.20 TN - A Homebrew Enabler supporting all PSPs with this firmware version.

GEN

 * 5.50 GEN - An update to Dark AleX's M33 custom firmware, secretly built from the source code of 5.00 M33. Adds PSN network support. Was known to be a bit unstable, and to screw up save games.
 * 5.03 GEN - A Homebrew Enabler for newer "unhackable" PSPs.

Dark AleX/M33

 * 5.00 M33 - The last and greatest version of Dark AleX's famous Custom Firmware. It is still considered the most stable firmware around to this day, and this version was still in use long after the disappearance of Dark AleX himself. 5.50 and 6.xx games have to be patched to run on this CFW, though not all games are supported.
 * 4.01 M33
 * 3.90 M33
 * 3.80 M33
 * 3.71 M33 - The first custom firmware supporting both PSP Fat and Slim.
 * 3.60 M33 - For PSP Slim only. The first custom firmware to run on the newer models.
 * 3.40 OE
 * 3.30 OE
 * 3.10 OE
 * 3.03 OE
 * 3.02 OE
 * 2.71 SE
 * 1.50 CFW Proof-of-Concept - The first Custom Firmware, ringing in a new era of PSP Homebrew.

Miscellaneous

 * Utopia - An attempt to create a fully open source and developer friendly kernel for the PSP. However, most developers found it easier to just work with existing Sony code, and any such kernel would be incompatible with existing PSP games and homebrew, so it never really took off. - Source Code