Available as an assembled Module and as a DIY project.
This Module is currently available.
MG ID: 57792
dual channel manual crossfader
crossway is dual channel manual crossfader with clever normalization in 4hp.
left and right channels are swapped so you have L/R and R/L crossfading.
of course you can use the individual inputs too.
channel 1L is normalled to a dc offset voltage, so you can also send out a cv while fading easily.