The master is 10.98 which is the best and most stable version.
But there are forks, people who use that as a base and downgrade to lower clients.
This looks like a pretty stable version of 8.6, based on TFS 1.2:
GitHub - ninjalulz/forgottenserver at 8.6
Other people play with the OTX server:
Releases · mattyx14/otxserver · GitHub
You can compile those to 8.6 as well, although OTX is known to be more experimental and unstable. Both of these alternatives are way better than what any 8+ year old 0.36 shit can give you.