Latest mCRL2 as of 26-10-2012 release: 201210.1.
Latest development version documentation is also available.
mCRL2 is a formal specification language with an associated toolset. The toolset can be used for modelling, validation and verification of concurrent systems and protocols. It can be run on Windows, Linux, Apple Mac OS X and FreeBSD.
The toolset supports a collection of tools for linearisation, simulation, state-space exploration and generation and tools to optimise and analyse specifications. Moreover, state spaces can be manipulated, visualised and analysed.