I played with an older version of it a few years back - it has a bit of a learning curve, but well worth the effort.

If you are into coding - there is an interesting tool out there for creating 3D CAD files using a software-based paradigm (that is, you "code" your object):

http://www.openscad.org/

If you prefer something browser based:

https://openjscad.org/

Also:

http://www.implicitcad.org/

Finally - if you want something closer to freecad (mouse/gui) but browser based:

http://shapesmith.net/

There are a few other solutions out there as well that are open source (and note - not all of the above can really be considered "CAD" in the strictest sense of the work - freecad is really the only one, honestly) - but these are the ones I can think of off the top of my head.