[FarmerPotato]

@Shift838 made a ready configurator for the 99/4A MESS. He calls it OoeyGooey.

You might also try running Classic 99 under WINE. That works on my x86 MacBook. Classic99 has the legal license to ship with ROMs. (Well PC99 as well but it's hard to get.)

I'm not sure if JS99er runs standalone --that's a very good emulation in the browser, which you can load up anytime.