bear1728

I've used https://cloud.sagemath.com/ with great success. Especially with writing Sage code, LaTeX, Python, Go, Javascript, and a bunch of others. It's especially nice since I can work on any of these collaboratively with others. Right now I'm using it with a small team writing a bunch of markdown files with math, which smc (sage math cloud) handles great.

https://cloud.sagemath.com/ has one of the best online latex editors I've seen. It has live preview and you can jump from source to the right position in the end product, and vis-versa. It's definitely worth checking out!