Same thing as Cocoa or the windowing API in User32.dll, but as a network-transparent client/server architecture (usually behind a library though, so doing thing

Same thing as Cocoa or the windowing API in User32.dll, but as a network-transparent client/server architecture (usually behind a library though, so doing things like opening a window is quite similar, except that Xlib isn't as ergonomic as Cocoa or even Win32).