Abstract State Machines (ASM), formerly known as Evolving Algebras, are a formal method for specification and verification. The approach was originally developed by Yuri Gurevich, based around the concept of an abstract state machine, and is also espoused by Egon Börger. ASM theory is the basis for Abstract State Machine Language by Microsoft and http://www.xasm.org XASM (Anlauff's eXtensible ASMs), an open source implementation.