Yes, the POSIX subsystem was pretty minimal (just base POSIX.1, the syscalls and basic standard library). But it sufficed to port a number of UNIX command-line utilities to NT.
SFU (the official abbreviation for Windows Services for UNIX) was reasonably capable, since it was initially based on MKS Toolkit and later on the Interix product repackaged by Microsoft. The first SFU release was 1999.
There were, of course, various third-party UNIX-on-Windows implementations besides MKS and Interix, most famously Cygwin but also for example Korn's UWIN. All of those date back to the 1990s.
WSL is just the new Linux-flavored version.
Biting the hand that feeds IT
