Gillespie is a project mainly written in Haskell, it's free.
Gillespie simulator
This package implement the direct method Gillespie's algorithm. It can be used for simulating biochemical reaction networks. See http://en.wikipedia.org/wiki/Gillespie_algorithm for more information.
$ cabal install mersenne-random-pure64 $ ghc -O2 --make simulation.hs $ ./simulation
This package depends on the package 'mersenne-random-pure64'.
To install it, make sure you have the package 'cabal-install' installed.
"The 'cabal' command-line program simplifies the process of managing Haskell software by automating the fetching, configuration, compilation and installation of Haskell libraries and programs."
The recommended way of getting 'cabal-install' is through the 'Haskell platform': http://hackage.haskell.org/platform/.
You can also install 'cabal-install' manually: http://hackage.haskell.org/package/cabal-install. If the bootstrap script complains about a missing 'time' library, install it manually: http://hackage.haskell.org/package/time-1.1.4 (cabal-install version 0.8.2. says it depends on time version < 1.2). (http://hackage.haskell.org/trac/hackage/ticket/743 and 744).
When you have 'cabal-install' installed and 'cabal' is in your path, do:
$ cabal update $ cabal install mersenne-random-pure64
As a third option, you can try to install 'mersenne-random-pure64' manually: http://hackage.haskell.org/package/mersenne-random-pure64.
$ ghc -O2 --make simulation.hs $ ./simulation
or (but much slower)
$ runhaskell simulation.hs