Very cool! This looks a lot like something Michael Chastain was working on in the late 90s: http://lwn.net/1999/0121/a/mec.html

It also is similar to GDB's record-and-reply functionality, except that I believe GDB is limited to a single process. I suspect that GDB's approach is much higher overhead also, because I think it actually records state changes for every instruction: http://sourceware.org/gdb/onlinedocs/gdb/Process-Record-and-...

Unlike the GDB functionality, this doesn't seem to support reverse-stepping. Hopefully this can be added -- it makes a huge difference when you can reverse-step backwards from the failure to find out where things went wrong: https://sourceware.org/gdb/onlinedocs/gdb/Reverse-Execution....