Right now there's no active public backends, there are a few prolific JJ contributors who are working on their own forge though (https://ersc.io https://ersc.io

Right now there's no active public backends, there are a few prolific JJ contributors who are working on their own forge though (https://ersc.io https://ersc.io). At Google, JJ is natively supported for interfacing with the monorepo, this is where the proof of being backend agnostic comes from. Hopefully as the network effects catches on we'll see more and more of a desire for 3P forges.