Short answer : Yes
As you might allready know, linux comes in many different versions, 1 of them is as you mention, Lindows.
Then you have the "mother" of Linux, Unix ( that also comes in differnet colours ).
We have BSD ( Open, Free, Net to mention some ) they also have a root in Unix, and has been used to make OS-X ( for Mac )
BeOS, still one of the ones I find "cutest"
DOS ( Disk Operative System ) from various sources, we had CP/M, anyone else remember this
OS/2 from IBM, Debian, Tao OS (now called Elate), KallistiOS ( an OS for Sega Dreamcast, fully functional ).
Palm OS and EPOC for handheld.
Of yes... someone claimed that there was an OS family, called Windows
It has more to it than just XP, like the Windows CE and Pocket PC that also is for handhelds.
And the list goes on and on ......
Here are some free OS's :
http://www.freeos.com/