Windows can be made to look similar to Unix, from a suitable vantage point and given sufficient use of green-tinted glasses. (I watched The Muppets' Wizard of Oz yesterday, and oddly enough this seems like a good analogy: we're definitely not in Kansas any more).
The background: SBCL is a lisp environment (native-code compiler plus runtime) which is fairly solidly Unix-centric, and has been for the best part of 20 years or so; at its inception, it also ran on a Mach kernel. Among the Unixisms pervading the code are simple things such as parsing filenames; mild things like having streams associated with fds (rather than HANDLEs); and fairly fundamental differences in signals, exceptions, and handlers. This latter is important because a fair amount of runtime support is implemented in terms of Unix signals: the garbage collection is assisted by a write barrier; the debugger wants to be able to set breakpoints by writing an illegal instruction at the start of a function; and so on.
Why is this relevant? Well, I'm staring at a 65-page diff from Alastair Bridgewater, containing a sufficiently-complete port of SBCL to Windows. ("sufficiently-complete" here means that it self-hosts and mostly doesn't crash-and-burn instantly; it certainly does not mean that it's stable enough to run your mission-critical server on; whether you'd want to do that on Windows in any case I leave open.) This is the second iteration of this patch; Juho Snellman has already blogged about the first iteration, which was eight pages shorter; this was not the direction I hoped the patch would go, but oh well: I am assured that the extra eight pages include extra functionality, and certainly there is a lot less that causes screams of horror.
Alastair's made patch and binaries of the latest attempt available, as well as the beginnings of a TODO list: if there are Lisp-interested Windows hackers out there, more eyes and hands would be very welcome.