The former is libre and gratis, runs as a standalone or plugin and in the browser!! and is based on the latter.
The latter has a libre and gratis standalone version, the plugin version is non-gratis.
I worked in music tech for a few startups starting in 2000, have written a few instruments (VSTs) and dabbled in making noise (some call it music). specialize in cutting edge dsp, but i just like applying it to PHAT SOUNDS. :D i'm a much better sw engineer DSP enthusiast than an artist, but can still hold my own.
Get ready for so much fun. Making music gets infinitely more fun once you start to build all your own tools =) Do you code? If you can code even a bit..
It's not my day job anymore, but send me an email if you'd like to know more, I guess I'm finally old enough to pass on some shit...
Take your time with modular. It’s easy to get carried away and overspend. Each module is deeper than it looks and you really benefit from getting to know each one.
Edit: and, of course, VCV Rack is the best.
I started getting in to this at the start of the year. Already had an old, dusty MicroKORG and MIDI interface to use it as a controller, but recently splashed out on a bigger controller as the Korg's tiny keys were hurting me - plus, I wanted something bigger to get better at piano!
A couple of free soft synths I'd recommend are Surge XT, and Vital.