COM/DCOM have offered a relatively usable solution for interprocess and cross-machine RPC for... quite a while. I used it to do interprocess communication back in the VB6 era (it was built-in), and in fact I did it by accident. I picked the wrong checkbox in the project options, so I ended up with the user interface of my application and the backend literally running in separate processes.

Other than the performance overhead (that I initially chalked up to 'oh, COM is just slow I guess'), the way I finally noticed was when a pointer I passed across the COM boundary wasn't valid (because it was to memory in another process). Whoops! Everything was working perfectly up until that point.

(FWIW, I am pretty sure the invalid pointer thing only happened because I was passing a raw address around - VB6 doesn't have pointer types.)

Plus, since COM provides ways to do source-level and binary compatibility, you can leverage that for your RPC.

I won't call it awesome, but it's quite robust and gets used in many places on Windows.

At a more basic level, you can trivially implement RPC using windows messages, though the security model improvements in 7 and 8 have made this a bit more complicated. There is excellent, straightforward infrastructure for establishing message loops and sending messages - really easy to get right - and it doesn't require your application to have UI. Pretty much any thread can receive and process messages if it wants to.