A few weeks ago I was planning to design a model I could send to a local 3d printer to replace a broken piece in the house for which I knew it would be impossible to find something that would fit exactly.

I looked around through a couple of open source/free offerings and all found them frustrating. Either the focus on easy of use was too limiting, the focus was too much on blob, clay-like modeling rather than strong parametric models (many online tools), or they were too pushy to make you pay, or the UI was not intuitive (FreeCAD).

OpenSCAD was the one which allowed me to get the model done, and I loved the code-first, parametric-first approach and way of thinking. But that said I also found POV-Ray enjoyable to play around with around the 2000s. Build123D looks interesting as well, thanks for recommending that.