Interestingly, Overleaf is open source [0], although I can't speak to how well the open source version works.
[0] https://github.com/overleaf/overleaf
IIRC, it is nerfed out. It is more open core than actual open source, and the paywalled features of the online version are missing.
alt Hacker News
IIRC, it is nerfed out. It is more open core than actual open source, and the paywalled features of the online version are missing.