I noticed that all the dependencies of TilEm were in tree, but TilEm itself was not. For those who don't know, TilEm is an emulator for z80-based TI calculators (such as the TI-82).
Created attachment 334064 [details]
I'm not entirely sure I got the ebuild perfectly correct (I'm fairly new to writing ebuilds), but it does compile and run here.
I've added this ebuild to https://github.com/tianon/gentoo-overlay/tree/master/app-emulation/tilem now, so it's easier for others to use and test, if they're so inclined.