With links for each, and sorted into categories. Largest category being finite element analysis (FEA) and computational fluid dynamics (CFD) simulation solvers which are used for things like stress, thermal, electromagnetic simulation etc. Also some CAD and general tools
There’s a professor and his research group at university of Michigan that does compliant mechanisms that u could check out if they’ve got something. It was a while ago that I applied there so possible he moved but still worth a check.
I’ve never used freecad as I’ve always had access to a cad program thru work. One option that’s not free is to join a maker space that has better cad programs or just torrent. But you’re definitely in need of FEA for the bistable part