Over the past years we have developed a.o. the mdata NoSQL database, which is stable and has been serving reliably in production since. It was implemented with Luajit, but since the release of qjs (QuickJS) we follow that direction instead, along with quite a bit of C development too.
Our current main project is the Community Post Office. It is a virtual place, analogous to a local post office, where people come and go (or meet and gossip) to exchange information, files etc. But then online. So instead of visits, we could call it online synchronizations. It also facilitates different kinds of information distribution flows, e.g. store and forward with other post offices. It is also prepared to serve its cooperative community in case of disaster response. The first heart of the Post Office suite was mbus, a small but powerful message router, using TCP. But this has been succeeded by Teleport, which uses UDP. At the moment we are alpha testing direct messaging using Teleport as a simple public reflector on the internet.
With HTTP + REST, thinking started of messages that were sent from one host and port to another host and port. That became the client/server model.
In decentralized we need to start thinking about messages that are sent from one peer to another, still using either TCP or UDP, but then using something that looks more like a router than a server. Also, instead of pushing content to people, we prefer to send notifications when something becomes available to them.
We are developing for Ubuntu and other Debian based linux systems.
On our radar is also:
JS developments of OCapN
https://www.ocapn.org/
the Hare language
https://blainsmith.com/articles/network-programming-with-hare/