We’ve built an extensive event system that is in alpha:
We currently do not have any rust components built, but the system follows ICRC-72 and we’re looking for community members that would be interested in building the rust equivalent of the motoko components we do have.
With the current tools we can build a watcher that will broadcast any detected events to any number of listeners. If your canister is rust and you just want to listen, you really just need to implement the subscriber side of things which includes registration(an IC call), listening for being assigned a broadcaster(just implement the icrc72_hadle_event endpoint and parse the event type) and then you can validate incoming calls from valid broadcasters and see when your event namespace comes across. At the end of the call you can send cycles back to the broadcaster to pay for the notification.