3D Tin is an excellent example of modern and capable in-browser tooling.
The project actually looks to have started back in April 2010 as a way for Jayesh Savli to learn about 3D graphics programming, and it’s come a long way since!
In addition to the usual features you’d expect from a 3D modelling tool, objects can be exported in a number of formats including those suitable for 3D printing. Nice.
If that weren’t enough there’s a strong community behind the project with plenty of free models to muck about with.. in case you hadn’t guessed from the mediocre composition in this post
Definitely check out the development blog if you’re curious about how this sort of project can evolve over time!