1. FreeVast was announced as a hack (reversing and decrypting), while some vidz could be found on youtube, before "a hacker crew" comes up with Memento especially for the Memor32-MC.
The project is called so here also,...
But it differs in the point, which started this project.
Bootleg said it already,...
2. There is no "difference". These a 2 parts of the "FreeVast"-Project here on PS2-Scene and Metagames.
FMCB is the evolved FreeVast/"Free-OSDatel"-Hack (which only started an ELF from MC).
FMCB has more features, like rejecting to a custom-hacked OSD/or non-hacked OSD, start ELFs (hacked OSD) and ESR-Disc through the OSD directly (with external ESR.ELF. Comes in next release,...), (Disc-)Fastboot, Buttonlaunch, but still with the Auto-Launch-ELF/Autoboot-ELF-Support.
Some options are supported hardcoded (if no Config-File is present) and some features need a CNF.
ESR is intended to run burned (and patched) DVD's, or grant other applications, to have access to these patched DVD-Rs.
ESR has a higher compatibility than, Memento.
It seems, it even have a higher compatibility, than HDL.
The patching for Memento and ESR-Discs is the same,...
(Edit: Like JNABK said,... The ESR-Patcher"s" are better.)
3. Well,... It could load burned and patched discs, like ESR,...
Memento has his own GUI-Replacement (and could start external ELFs).
FMCB has the OSD-Hack and still could start external ELFs,... ^^
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux