I've always thought it would be nice if the kernel exposed this ability to regular userland applications. On Unix systems, Ctrl+Z of a terminal application will suspend it, but not across reboots. Core files are very close, yet typically they are only produced in response to a crash, and aren't really meant for resuming a process. Obviously there's lots of limitations (eg shared memory could cause issues, hardware states could change), but for a lot of cases it would probably work pretty well.

Not only is it great for triggering crashes, but if you then broke out into a debugger, you could toy with toggling register and memory contents and then single-step through the instructions to see what happens. It's really substantially easier to debug software under emulation because of features like these.