I know that most people are building variable fonts from inside their font editing software, but if your chosen font editing software doesn't provide good variable font creation tooling, you're left fiddling around with designspace files and fontmake.
If that's you, you may want to look at a new piece of software I've written called Pilcrow
, which is essentially a graphical user interface to creating designspace files and running them through fontmake with the appropriate options.
It works on Mac OS, Linux, and probably Windows if you have a Python installation and infinite patience. It's pre-release at this stage, so please give it a go and kick the tires, and let me know via the issue tracker
if it does something it shouldn't or doesn't do something it should.