Intel IA-32 architecture a.k.a. x86 offers hardware task switching capabilities since 80386. It includes TR (task register), memory segmentation features such as Task State Segment, task gates, call gates etc. However, this capability is not used in modern OSes which perform context management differently (for numerous reasons). Largely, the hardware task switching is not favored by any modern CPU architecture, not just x86. Within modern x86 OSes, only rudimentary TSS usage (that could not be avoided) can be found.
I am looking for information about which historical or maybe modern operating systems, both small and large, niche or general purpose, use hardware task switching. I am aware that Linux kernel up to 1.3 used it. I could not found reliable information about the MS DOS and Windows families, but I suspect some early versions of them are bound to use TSS at its fullest.