Ramping up to 100V in a 'Flex Module' sized board is quite challenging. I originally worked with LT to develop the current follower design. Powering a low current 100V source is challenging. I am still researching designs, but I have found multistage efficient design that is around 1200mm^2+. Trying to shrink that a bit more.
5V ~2.8A in
TPS55330 128mm $2.88 91% 5V-20V .6A
TPS40210 778mm $5.45 89% 20V-100V 0.08A
100V 0.08A per channel is often quoted for TENS. Since most manufacturers are more marketing than reality, I'll take their power specs with a grain of salt. We might be able to product the 4 standard TENS channels from one supply.
Any software related will be released under BSD or MIT license. SAAS or cloud based software will be AGPL.