Cumulus is available from the physical DVD version of Computer Music Magazine.
It's a granular sampler, run by a sequencer. The sequencer has 8 playable scenes, you can play one scene at a time. Each scene is a location within the sample, plus 12 parameters such as pitch, speed, size and jitter.
I really like the user interface, there's a different color for each scene, and you can easily see how the sequence proceeds through the scenes.
Fragmental is a good free multi-FX for FSU exploration. There are 6 FXs, and you can easily re-route them in real-time to serial, parallel or a mix of serial and parallel. The 3 most interesting FXs are spectral: Transpose, Exaggerate and Accumulate.
DtBlkFx is a superb spectral processor, and it's free! It has about 30 different algorithms. You can process as many as 8 algorithms in a series, but usually 1 algorithm is enough.
It reminds me of Native Instrument's discontinued Spectral Delay.
The UI shows a nice sonogram of both the original input and DtBlkFx's output. There is a Delay between the input and the output, this value defaults to 1 beat, but you can reduce that so it's almost instantaneous.
The documentation appears well done. I just goofed with parameters until I figured it out.
The UI is somewhat unusual regarding how to adjust coarse and fine values, but it's actually convenient when you get used to it.