IR blaster for smartphones. I still have one on mine and I can use it for tons of stuff, not just as a TV remote.
I even worked for a company who made lots of IR based products (taps/faucets, accessibility stuff) and it was amazing how many people had to buy the dedicated remotes for these products for extra money.
When I asked them if their phone has an IR blaster, so they could just download a free app and use it instead. "I have an iPhone" was the most common answer.
There are small and cheap USB-C IR dongles around nowadays - generally USB-C has been a blessing for making additional hardware features available on smartphones.
My current phone does have IR - though I'm not really using it much since most of the existing Android software for that is horrible (broken, ad-infested, requires account and access to everything, ..), and I have too many open projects to start another one for writing my own software for that.