Helm synthesizer review: It's the best free synth, and it runs on Linux too
Helm is the prime choice if you want the pure signal of Serum but don't care for the price. It's not a wavetable synth, but it does set modulations in a way that's similarly intuitive to Serum. You click the helmet by the modulator and drag the little green bars on the thing you want to modulate. They shift in time with the music at the depth you set.
This is probably the best synth you'll find if you prefer an open source workflow. It runs on Windows, Mac, and Linux, and it's open source if you want to take a shot at porting it to something else, or you just want to tinker.
Rather than talk your ear off about its features, I'll let you listen to some presets I made with it. $10 members can get these presets to use in their own music!
Helm has a unison and detuning option on its two main oscillators like Serum, so it's similarly easy to make a supersaw. Sharpen the envelope and you have superpluck!
It's also very, very, very good at sound effects. So good that you'll accidentally make them while trying to make something else. Embrace it. Have a haunted forest.
You can get these two presets and the MIDIs by becoming a member.