Did Windows ever support any hardware architectures other than x86?

Microsoft released Windows NT 3.1 in 1993 as the first purely 32-bit version of Windows.

Windows NT was developed as a multi-architecture operating system. Initially supported different CPU architectures, including IA-32, DEC Alpha, MIPS, and PowerPC.

The original idea was to have a common code base with a custom Hardware Abstraction Layer (HAL) for each platform. However, support for MIPS, Alpha, and PowerPC was later dropped in Windows 2000.

As far as I know there are 8 base-architectures (and a number of sub-variants) of which only 2 are still supported today with Windows 10.

Windows 1.0 to 3.11, Windows 95, 98 and Millenium Edition

x86 (16 bit and 32 bit variants, including 8086, 80186, 80286, 80386, 80486, Pentium, Pentium Pro, Pentium II, Pentium III, P4, Core, Core Duo, Core-I and various Celeron and Atom designs.) This also includes various compatible AMD and NEC CPU's.

Windows CE

MIPS, x86, ARM (thanks @pjc50).
(Not sure if CE ever ran on Alpha, PowerPC.)

Windows NT

x86, x64 (or amd64, both names are used), MIPS, Alpha, IA32, IA64, PowerPC.
Support for MIPS, Alpha and PowerPC was dropped in Windows 2000. Itanium was server only starting with Windows 2000 and 32-bit (IA32) was dropped for 2008 and 64-bit (IA64) with Server 2012 if I recall correctly. Only x86 (limited to some specialty netbook/tablet devices) and x64 are currently still valid for Windows 10.

Windows Phone

ARM, (maybe also MIPS ?)

Windows 10 for IoT

x64, ARM

Windows XP 64bit and Windows Server 2003-2008R2 support the Intel Itanium IA-64 architecture.