I use QCAD occasionally which falls into this category

  https://www.qcad.org/

The author provides downloadable versions for Windows, Mac and Linux and the source is available on Github if you want to build it yourself or provide bugfixes or extra features. He provides some features as extensions in a trial mode which ends after 15mins or so or you can disable them. Its pretty neat and to be honest the price for the full version does not seem to be that much though the community edition has always been sufficient for my needs and has enabled me to contribute with bugs/fixes/features.