alt Hacker NewsCould you elaborate on what you mean? My understanding of the Cocoa event loop was that ultimately everything is received as an NSEvent at the application layer (maybe that's wrong though).
Do you mean that you can just AXUIElementPerformAction once you have a reference to it and the OS will internally synthesize the right type of event, even if it's not in the foreground?
yes you can do a lot background UI interaction using the AX APIs. Displaying a second cursor is also simple, just a borderless, transparent window that moves around.
For the few things you cannot achieve with the Accessibility API's there are ways to post events directly to an app - even though CGEventPostToPid is mostly broken when used on its own. These require a combination of CGEventPostToPid and CGEventTapCreateForPid. (I have done a lot of this stuff in my BetterTouchTool app)