They seem to use two projects: Irwin: https://github.com/clarkerubber/irwin https://github.com/clarkerubber/irwin Kaladin: https://github.com/lichess-org/kala

They seem to use two projects: Irwin: https://github.com/clarkerubber/irwin https://github.com/clarkerubber/irwin Kaladin: https://github.com/lichess-org/kaladin https://github.com/lichess-org/kaladin