The RG280V is a handheld retro game emulator that is really tiny. It’ll handle everything up to PS1 easily, and some have gotten it to do n64, though not well.
I got it because I think PICO-8 games are really cute but are harder to love because they aren’t physical1. tac08 is an emulator that lets you play them on this lil’ guy. Lots of older reviews mention that the sound doesn’t work; it’s been updated and I have had no problems with it.
Another thing I really like are indie “Game Boy” games, that are made to be distributed digitally and played on an emulator. I’ve poked around at playing them in the browser before, but it’s a lot more fun with buttons and such. It’s cool to be able to get on itch.io and toss people a couple bucks for little weird arty experiments.
The RG280V costs $70 as of writing this at Retromimi, and $10-20 extra if you want to get it on Amazon. People say it’s the fancier version of the LDK emulator which has a similar form factor. If you want Android based, more power, bigger screen, and different form factor, everyone right now says the Retroid Pocket 2 is the best… but it’s not as small. With the varying screen aspect ratios of different emulated systems, the size of the screen you’ll play on is often going to be smaller than the physical display, so getting The Teeniest Thing Possible isn’t for everyone.
I was thinking about getting the Retroid Pocket 2 because it can be plugged into the TV and it can do netplay… but then ultimately I realized 90% of what I’m going to want one of these for is tiny indie games, and I don’t have anyone who’d want to play multiplayer anyway.