Games

https://gitlab.com/megamanlegends - Mega Man Legends 1 and 2 various tools (asset extraction, save state browsing etc.).

https://tetracorp.github.io/tokimeki-memorial/ - Tokimeki Memorial reverse-engineering articles. Contains a lot of useful info on how to get started with PSX reverse engineering.

https://github.com/AliveTeam/alive_reversing - Re-implementation of Oddworld: Abe's Exoddus and Oddworld: Abe's Oddysee.

https://github.com/ChrisNonyminus/mml1 - WIP Decompilation of Megaman Legends (aka Rockman Dash) for the PlayStation 1.

https://github.com/Erick194/PSXDOOM-RE - Doom-RE.

https://github.com/FedericoMilesi/soul-re - Reverse-engineering project of the 1999 PlayStation game Legacy of Kain: Soul Reaver, from MIPS to C.

https://github.com/FoxdieTeam/mgs_reversing - Metal Gear Solid PSX reimpl repo.

https://github.com/Gh0stBlade/KAIN2 - Legacy of Kain: Soul Reaver Decompile.

https://github.com/OpenDriver2/REDRIVER2 - Driver 2 Playstation game reverse engineering effort.

https://github.com/OpenNFS/NFSHSX - Need for Speed: High Stakes Disassembly translated to C source code.

https://github.com/TOMB5/TOMB5 - Tomb Raider: Chronicles Disassembly translated to C source code.

https://github.com/Xeeynamo/sotn-decomp - Decompilation of Castlevania: Symphony of the Night (PSX+Saturn).

https://github.com/open-ribbon/open-ribbon - vib-ribbon decompilation (PAL version).

Game tools, documentation etc.

https://github.com/rickomax/psxprev - PSXPREV - Playstation (PSX) Files Previewer/Extractor. Supports many model, texture and animation formats from various games.

https://github.com/CTR-tools/CTR-tools - Crash Team Racing (PS1) tools.

https://github.com/AdrianoDiDio/Medal-Of-Honor-PSX-File-Viewer - A set of tools to open and view files from the PSX games Medal Of Honor And Medal Of Honor:Underground.

https://github.com/IvanDSM/KingsFieldRE - King's Field (II) Reverse Engineering Tools and Documentation.

Hardware, tools

https://github.com/JaCzekanski/ps1-tests - Collection of PlayStation 1 tests for emulator development

https://github.com/ogamespec/psxdev - Sony PlayStation chips reverse engineering.

https://github.com/Laxer3a/MDEC - Attempt to verilog Implementation of Playstation 1 (PSX) chips.

https://github.com/pgate1/PlayStation_on_FPGA - Playstation on an FPGA

https://github.com/emvivre/Sony-PS1-executable-disassembler - Simple disassembler of Sony Playstation executable (MIPS R3000A instruction set).

https://github.com/Happy-Ferret/sym - Parse Playstation 1 symbol files (*.SYM).

https://github.com/infval/SlowR3KA - PlayStation 1 Disassembler (MIPS R3000A)

https://github.com/MonstersGoBoom/mips32 - mips32 disassembler and maybe emulator at some point

https://macrox.gshi.org/The%20Hacking%20Text.htm - The secrets of professional gameshark hacking

https://github.com/lab313ru/ghidra_psx_ldr - Sony Playstation PSX executables loader for GHIDRA