Bagatur is an open source chess engine.
This means a program, which can play chess.
The ELO of the latest version 1.3a is ~2300, which is based one the public computer tournaments.
All version and ratings of Bagatur, which are tested by computerchess.org could be found here.
Open source project is hosted at sourceforge, where you can find everything relevant:
Downloads, Reviews, Q & A, Programming code, etc.
It hasn't its own user interface and uses arbitrary UCI user interfaces like Arena.
The program is released under EPL license.