Zurichess is an open source chess engine. Its current strength is around 2820 Elo on CCRL 40/40 which is around 2700 Elo on a regular human scale. The engine supports adjustable strength so the average chess player can still beat it.
You can play online against Zurichess on the Free Internet Chess Server.
The latest stable version is available as an Archlinux AUR package at aur.archlinux.org/packages/zurichess/.
I like it a lot (a unique human-like playing style)! - Brendan, Chess&Cognac.
Zurichess is an open source chess engine which means that you can read the code, modify it or use it in your own projects. The engine is written in Go and can be used as a library for board setup, FEN and EPD parsing, or position evaluation.
Before sending your first patch see the contribution guidelines.
For feature requests and bug reports, check out the source repository at bitbucket.org/zurichess/zurichess.