In no particular order
Only including those which support connected sessions, i.e. not APRS-only
| KISSet | https://github.com/piemmm/KISSet |
| BPQ32 | https://github.com/g8bpq/linbpq |
| xrouter / xrpi | https://wiki.oarc.uk/packet:xrouter |
| Linux kernel | https://github.com/torvalds/linux/tree/master/net/ax25 |
| Dire Wolf (via its AGW interface) | https://github.com/wb2osz/direwolf |
| AGW PE | https://www.sv2agw.com/Home/downloads |
| ax25embed | https://github.com/isomer/ax25embed |
| rax25 (rust lib) | https://github.com/ThomasHabets/rax25 |
| patty | https://scm.xan.host/patty.git/ |
AX.25 Link Access Protocol for Amateur Packet Radio v2.2, revision 10 September 2017
AX.25 Link Access Protocol for Amateur Packet Radio v2.2, revision July 1998
AX.25 Amateur Packet-Radio Link-Layer Protocol, v2.0, October 1984
Notes section of https://github.com/isomer/ax25embed/blob/main/ax25/ax25_dl.c
Search for 2017 and/or 1998 within https://github.com/ThomasHabets/rax25/blob/main/src/state.rs