Hello, I'm a golang developer, and I wanted to learn/play a little about revs from lineage, I didn't find anything about rev free from essence eva or assasin, is there any open source project?

I wanted to learn to build in some way.

You can get Essence Assassin from free L2jMobius branch:
https://bitbucket.org/MobiusDev/l2j_mobius/src/master/L2J_Mobius_Essence_7.1_Assassin/
Note it's a bit outdated and paid members get updates and support, also access to newer branches 🙂 

Edited June 28, 20242 yr by L2LIVEpro