It's a Linux-based firmware for RG405M RG405V and RP2+. There is not HW acceleration for now, but the author managed to make audio working (it's quite hard for UNISOC chips!). It would be so great to have fully working Linux-based operating system on these devices!
I just installed garlic the other day on a 405M. However, I’m also trying a retro pocket 3+ and I think I may return the 405M, anyway. The 405M is very nice, but the metal case is very slippery and my unit has pretty noticeable LED bleed.