RuneLit is a fork of RuneLite that provides more functionality and less restrictions while staying open source. This is meant to directly compete with 3rd party RL clients that are trying to sell their code.

Notable Features:

Auto patch-time Bytecode patcher

What a mouthful right? it's great though.
The heart of the auto patching system is ByteCodePatcher. Adding a new patch would go as follows.

1. Find unique identifier for class so it can be found after rev update, Add check to ByteCodePatcher.
2. Create Transformer for rsClass and call it when class is identified.

A fully functional example is included at ActorTransform:
transformGetAnimation removes filtering
transformAnimationChanged removes filtering