https://www.sharelatex.com/

[corvini-sdd]

In https://github.com/att/rcloud/wiki/Similar-tools it is stated that https://www.sharelatex.com/ is not open source.
Since 2020 when this was written sharelatex merged with overleaf: https://www.overleaf.com/blog/sharelatex-joins-overleaf-2017-07-20
And overleaf IS open source: https://github.com/overleaf/toolkit/

Thought I'd let you know.