Yeah, I was wondering that - it wasn't Windows, but it had Windows applications
Depending on how far back, that could leave a few choices:
If it's more recent--within the past couple of years,, it could be ReactOS, Linux (with Crossover Office), eComStation (the current available successor to OS/2 Warp) or QEMU.
If it's back a ways, my guess would be OS/2. MS did joint work with IBM on developing OS/2 in the late '80's and early '90's, but dropped OS/2 in favor of developing Windows. IBM continued to develop it well into the mid-1990's, and stopped selling it last December.
Oh I see, thanks.