zefie's unofficial BAE resources:

• zefie's BeatnikX Player (C# Windows-Only wrapper around the old ActiveX Plugin) (source code)
• zefie's unofficial libMiniBAE & playbae (source code)
• Browse Media Content (RMF, MIDIs, and PatchBanks)

Original MacOS SoundMusicSys useful resources:

• A helpful StackExchange thread
• fuzziqersoftware's Classic Mac OS resource fork disassembler
• Old SoundMusicSystem.h Include (from Blzut3/Wolf3D-Mac but made easier to read online)

miniBAE and newer useful resources:

• heyigor/miniBAE (Official miniBAE source code)
• zefie's Discord (join the #beatnik channel for discussion)
• miniBAE LPCwiki Article
• MobileBAE LPCwiki article
• Beatnik Mobile Sound Builder (based on mobileBAE - includes XMF file creation tool and player)
• SF2 conversions of the generic mobileBAE soundbanks

Other stuff:

• Who is zefie?
• Support on Patreon