I believe dark fi will serve as a perfect compliment to Nostr. Not that they will be used together, but one for public, one for private. I am also fond of Qortal

DarkFi also recently announced they will be using POW randomx rather than POS. Also, another project i love, tho people fud the hell out of it, is Pirate Chain. A fork of Zcash with shielded transactions by default. Very fast transaction times.