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.

Sounds like you're looking for the checkpoint/restore functionality that has been in the works for a few years now. Check out http://en.wikipedia.org/wiki/CRIU for more details, seems they have things mostly working now.

DragonFly BSD does this. They call it process checkpointing.

Processes under DragonFly may be "checkpointed" or suspended to disk at any time. They may later be resumed on the originating system, or another system by "thawing" them.

http://www.dragonflybsd.org/features/#index8h2

OpenBSD and FreeBSD call it suspend/resume I think:

http://openbsd.org/papers/zzz.pdf

http://wiki.freebsd.org/SuspendResume

Those links are talking about suspend/resume of the computer, which is a totally different thing.

You might enjoy rr, 'record-replay', which works kind of like gdb (and I believe is based on it) after you record a program execution --- you can then use gdb multiple times on the stream of execution. rr-project.org.