alt Hacker News> BOSL2 ... but it is an extra set of functions you need to remember sadly
It's also extremely slow: it implements chamfers and fillets using morpho, and if you have a large number of fillets, the morpho algorithms (minkowski / hull) are very much non linear in time on polygonal meshes, which leads to compute time explosion if you want a visually smooth result.
you can get around this somewhat by having less visually smooth previews when editing and higher quality when you want an stl