helm is an open source synthesizer available as standalone , vst and lv2 available for all platforms ( linux, windows, macos)
helm home page
is it very easy to use and fun, the gui is very nice, easiest to use than zynaddsubfx for a beginner like me
you can download it as a debian package helm download deb
or with git
helm git
i tried to compile it for solus but got an error : make[1]: * [Makefile:430: build/intermediate/Release/border_bounds_constrainer_b5a34af8.o] Error 1,make: * [Makefile:85: vst] Error 2
thank you