Maude is a high-performance reflective language and system supporting both
equational and rewriting logic specification and programming for a wide
range of applications.
Maude has been influenced in important ways by the OBJ3 language, which can
be regarded as an equational logic sublanguage.
Besides supporting equational specification and programming, Maude also
supports rewriting logic computation.

Homepage:
http://maude.cs.uiuc.edu/
