For a long time I've been using Noisemagic NMT-3 with my NAS. The controller board is tiny, fits in the corner of a 120mm fan, has a wire thermal probe which I tape to my hottest drive.
At 30C it runs fans at 5v then ramps up to 12v at 42c max. This is perfect for my use case since that is the ideal range for hard drive temps. Allows my fans to dynamically run dead silent in cooler days and high rpm during hot summer or data scrub task.
However, the company is out of business (noisemagic.de). This is the NMT-2 model listed on a reseller page. I can't find any other links for NMT-3. Bought mine from frozenpc many many years ago. Only difference is the NMT-3 has a external wire probe.
What options are the for fan controlling? Most of the ones I see now are either very bulky large, manual knob/dials or require installed software to control.