Beads is a tracked mutable state language. It used the State-Action-Model pattern (see sam.js.org), and is built from the start to support time travel debugging. Unlike `rr` and its sequel `pernosco`, it is not an instruction level reversibility, but a state change stepwise reversibility, which is efficient enough to stick around and be used in production use (not just in the lab).

There is a "blackbox_write' and 'blackbox_send" feature, which allows you to send session information sufficient to replay the user's session for debugging purposes.

This is a very powerful feature, and one that we are seeing more and more efforts to offer, because in a world with so many computers, being able to reproduce rarely occurring, data-dependent bugs, is very important.