No love for FreeCad? It's certainly comparable to other desktop software for simple designs. The constraint solver is actually better than several I've used.
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):
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.
