This is a v-trig driven 2 or 3 way switch. The 2/3 step selection is determined by patching an output from the 3rd step.
I use a pair of these to extend the 960 sequencers but it has other applications. It switches control voltages so can be used for switching between modulation sources like ADSRs. I have these in a large rig based on the Moog IIIp. I had the original Moog back in the day and these little eurorack clones work the same, are well built, smaller and cheaper. As it is driven by the rising edge of a v-trig you could use it with other systems. It works well with my Doepfer rig too. If you have a 960 sequencer you definitely need one of these.