The problems about many of these free GitHub based project is that they requires extra knowledge in regard to setup, if they are not already browser-based.
As we are talking of free tools that make for good companions, I can highly recommend:
Renoise - Has a trial (no time limit) and the integrated sample editor allows you to create/draw/build your own single cycle waveforms. Spice things up by adding an FX Chain and bake it into the sample. And of course export them as .wav.
Vital - Free VST/Standalone synth. Often compared to Phaseplant. Has an integrated wavetable editor that is easy to use. Tip: use your single cycle waveforms in here to create wavetables.
Ocenaudio - A free and easy to use Sample Editor alternative to all the other stuff out there.
Was considering writing or making a tutorial if that is of interest to anyone.
I love Renoise as DAW software. I ran a cracked version for very long time and at a certain time, I just bought the full licence due to that I was very happy about it and didnt want to wait for the latest version to get cracked too