Nettle

The concept of scanned synth is less well known and there are no manual for it so it might be hard to get start with it. However there are not so many parameters so after a few tweaks with the presets you can get the idea rather intuitively.

The builtin HPF/LPF is limited that an external EQ is required to produce good sound, and I recommend also replace the builtin reverb by a better one. It can also benefit from a chorus effect plugin. The sound it can produce is noisy but warm, and can make very intrigued sound. A very creative free plugin indeed.