This one is recursive-grid for Hammerspoon users on macOS, and is probably the easiest of the open source implementations to fully customize. (I made it years ago)
I researched many different varint encodings for a GraphQL-specific binary format (resulting in Argo: https://github.com/msolomon/argo ). I ended up choosing protobuf-style zig-zag varints, but I also found these interesting:
This one is recursive-grid for Hammerspoon users on macOS, and is probably the easiest of the open source implementations to fully customize. (I made it years ago)