Gnash is the FLOSS software that can be used to run potlatch. Because I(User:Logictheo) want to help a developer of Potlatch to compile it on their Operating System of choice which happens to be the OS X Operating System (which is not FLOSS). I'm planning to research how that can be done by posting relevant information.
Mailing list references
I guess and I think it is logical for Richard not to have time to spend to learn how to compile Gnash on his OS, so since I myself have a lot of free time I can use it to ask for help. These are past 'asking for help' mails on the Gnash mailing list regarding compiling on OS X 10.4.