yeah, speedfan with suitable motherboard headers will take you far. Ultimately whatever software you can use will be determined by the hardware you’re using, unless you’re willing to go full diy. fwiw, CAM is an improvement on corsair link. i tried the GRID hardware controller but it doesn’t support PWM.
If you’re up for it, also look at SIV; it’s a 3rd party package for monitoring and configuring controllers used in all sorts of hardware. I ended up using it to configure my corsair link kit and the author is active on the corsair forum. It’s fugly as hell but works better and you only ue it to config, you don’t have to keep it running. It might support at least some of the NZXT kit but i haven’t tried it with it.
Then i suppose you could look at building your own; plenty of small SoC boards can support PWM output and whatever sensors you need. then the software interface is whatever you can make it