Download of Cain 1.10 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. Cain for Mac lies within Education Tools, more precisely Science. We recommend checking the downloaded files with any free antivirus. The actual developer of this free software for Mac is Sean Mauch.
From the developer:
Cain performs stochastic and deterministic simulations of chemical reactions. It can spawn multiple simulation processes to utilize multi-core computers. It stores models, simulation parameters, and simulation results in an XML format. In addition, SBML models can be imported and exported. The models and simulation parameters can be read from input files or edited within the program.
You may want to check out more software for Mac, such as Cognition Episode 4: The Cain Killer, which might be similar to Cain.