BirdBrain was an e-mail proof server for problems in combinatory logic. It was built by Ross Overbeek in 1986 with inspiration from Raymond Smullyan's To Mock a Mockingbird (Knopf, 1985).

People could send e-mail containing a conjecture in combinatory logic, the problem would be given to the theorem prover ITP, and the results of the search would be returned by e-mail, all without human intervention.

See "A Note on Smullyan's Birds", by Overbeek and Glickfeld, Association of Automated Reasoning Newsletter #7, October 1986.