Boss RSD-10 by I.F.
The RSD-10 is a member of Boss' "Micro Rack" family of half-rack effect units from the 80's (in case the decade wasn't obvious from the color scheme). One of my biggest regrets is selling the RDD-20 I had when I was in high school. The Micro Rack units were all fantastic, but the hidden gem of this golden age of Boss effects is the RSD-10. The RSD is, as far as I know, the only standalone effect unit that will listen to the pitch of an audio signal from a 1/4" jack and turn that pitch info into delay time or sample pitch info.
Now you're going to say - but you can totally just run your guitar into a pitch-to-MIDI converter and then control whatever you want with whatever pitch. Well, that's true, but the RSD is the glitchiest thing ever to be made, and when it tracks your pitch, it totally freaks out.
The RSD has two modes of operation: a delay with several different max times selectable, up to 2 seconds, and a sampler with two modes of record and playback. The two recording modes are auto-record and triggered record/overdub. The two playback modes are triggered playback and gated playback, the latter allowing for pitch bending and control of dynamics. The pitch tracking feature serves basically the same function in both delay and sampler modes - setting the speed of the repeats/samples.
What makes the pitch tracking great is it's glitchiness, resulting from the fact that it's only designed to track pitches between C5 and C7. That equates to just about everything above the 12th fret on the B string of the guitar, which isn't a lot, and it can't track chords. It basically just picks the loudest overtone present in a chord and uses that as the pitch. When you feed it anything below (or above) it's "designated" range, it gets weird, in the best way. Super long delay times and bit-stretched samples are just the beginning. Since it assigns the root pitch position of the sample by listening to the pitch key input while recording, any riff you record will be arpeggiated by itself if you play the same thing into the pitch key as the audio input while recording. It gets pretty nuts real quick.
I gave it a 2 for "ease of use" for two reasons. First of all, when in bypass mode, it switches to passing the pitch key input to the output, blending it with the input signal. This is annoying if, like me, you feed the pitch key a less-effected or re-pitched version of the guitar signal, which brings me to my second issue. The guitar signal has to be split into three separate signals to operate the RSD: audio input, pitch key input, and gate trigger input. Preferably, the pitch key input has some kind of pitch shifter going into it, while the gate trigger benefits greatly from compression and boosting. And then you've got to handle make-up gain from splitting the signal, unless you use a mixer, which gets even more gear involved in the use of a single effect.
But, I feel like there's nothing I've ever heard that sounds quite like the RSD. It's definitely one of the craziest, but still most controllable effects I've used. I've got a Digitech Space Station and a Red Panda Particle, among other oddballs on my pedalboard, and the RSD-10 will definitely hold it's own against them in an alien invasion sounds contest any day.