Are there any 'smart' ejection seats that eject automatically when an engine failure occurs or the aircraft gets into to a stall that can't be gotten out of, to save the pilot the decision of whether s/he should try and save the aircraft?
The Soviet Yakovlev Yak-38 (and also the Yakovlev Yak-141) had an automatic ejection seat. The aircraft had two smaller engines for VTOL. If one of them failed, the seat ejected automatically once the aircraft rolled past 60$^\circ$. From airvectors.net:
The pilot sat on a K-36VM ejection seat, with the ejection performed automatically in takeoff or landing excursions using an "SK-EM" system. The SK-EM system was automatically engaged after the aircraft rose a few meters from the deck; it could be turned off manually, or would turn itself off if the vectored-thrust nozzles were more than 67 degrees to the vertical.
These ejection seats were first developed for Yakovlev Yak-36 (though never installed on them). The Yak- 36 had two side-by-engines, the failure of any one of which could flip the aircraft- this led to the development of an automatic ejection system that would activate aircraft seemed to be departing from safe vertical-flight parameters.
According to ejection-history.org.uk, 18 automatic ejections have been recorded in Yak-38s.