Helium was interesting, but they locked it down so you can only use their proprietary hardware for access points, it seems kinda scammy.

IPFS is used by several archive projects like Anna's archive and libgen.

Meshtastic is a distributed local mesh network for text messaging.

Meshtastic
BOINC
Tor
I2P

Just off the top of my head. Meshtastic is probably the most similar to Helium but I don't know what Helium is and their landing page makes me not want to. BOINC supports projects not in the official lists, just google around.

Ipfs is a really cool useful project.

Filecoin is cool for super cheap longterm cold archives

Helium is well. I have mixed feelings about it.

Akashnet is a cool decentralized marketplace for docker container deployments.

There are a few peer to peer decentralized vpn things here and there.

There are tons of projects that are cool in concept but I really have to say you are more likely than not to lose money if you speculate on any tokens attached to the projects.

The folding at home folks have been going for a very long time now and that's contributed a lot to various fields of medicine over the years.

https://foldingathome.org/

I think nostr is the better decentralised social media technology, but I fear you might feel left out by the people that frequent it (as they would here).

Helium only allows their own insanely expensive hardware which instantly makes it seem pointless to use.

You could look at http://warrior.archiveteam.org/ and https://github.com/ArchiveBox/good-karma-kit

I2p?

Cool thread idea! TOR has already been mentioned, a relay seems to be save to run in most of the world.

This thread recently popped up and had some other nice ideas: https://lemmy.ca/post/40649656