needs only a day or two to implement

I think what comes closest to what you’re asking about is ham radio, officially called amateur radio. This is a hobby practiced by just a few million people worldwide, with approximately 800 000 licensed operators in the USA.

To participate, you need a license, for which you take an exam. This usually involves topics like frequency ranges, callsign prefixes, legal safety restrictions for radio equipment, and so on. There are normally 3 tiers of ham radio license, with each having a more difficult exam, but allowing more.

Once you have a license, you get a callsign, that identifies you worldwide when you’re talking to other ham radio operators.

For equipment you’d probably want to either start with a Baofeng handheld radio. This would be VHF/UHF only, so basically just line of sight for range, but ask your local club and you should find plenty of fun things to do with it. The advantage of this is, it’s literally dirt cheap like $10-20, iirc.

Or, if you’re looking to spend more money, you could get a shortwave transciever. There are many different ones, so I can’t recommend a specific one. Shortwave, or HF, will, if the weather is just right, reach around the world.

It’s a fun hobby, if you have the time, I suggest you give it a try!

(Assuming I stay in the Milky Way.) I’d use Saggitarius A* (the black hole at the centre of the Milky Way).

For directions I’d use coreward/rimward, spinward/trailing and zenith/nadir, as suggested by Winchell Chung.

For the OpenStreetMap, have a look at StreetComplete.

It shows you incomplete and missing things on the OSM near you, and lets you fill it in by answering simple questions. It has a little gamefication by giving you points for everything you fill in. Its really easy to use, which makes it quite fun, and you can make it a bit competetive if you want to.

Up/Downvotes usernames are publicly visible via the API to everyone. Kbin shows users this, lemmy does not.