I haven't tried these so I cannot comment on their quality. But this has a list. Of particular note is RetroArch, OpenEMU, and Gens as three FOSS options.
Edit: Also, alternativeto.net is usually a decent source for finding alternatives for specific software. Here's the list for Kega Fusion alternatives. This has some more options than the other link I provided.
Not only that, but it comes off as some weird replacement kid for their dead son. The Pitch Meeting is fun