Norix‘s NES/Famicom emulator VirtuaNES has been ported to the Nintendo 3DS by bubble2k16.

It used to be considered one of the best emulators before FCE and Nestopia, and it runs quite fast for lower spec-ed computers (at the cost of some emulation accuracy). But because of that, the Old 3DS / 2DS is able to benefit from this fast running emulator core. This runs full speed on an old 3DS / 2DS with support for tonnes of mappers. Although it doesn’t support every single mapper, the library of games that can run on this are probably fairly huge already.

Thanks to Nintendomax for the hint!