I found a cool free bass synth: Bass One by Daze Sounds.
It looks small and simple, but it has a big, fat sound. I crawled through the presets, and even though there’s only a handful of them, most of them are very useful in electronic music production. And of course, you can design more by yourself.
A quickstart guide is included to get you up and running.
Check the video for some example sounds.
There’s also a bunch of other freebies on the site!