Not a US start-up but I'll put it here for lack of another spot. Coral Jet, a planned A320 operator in Bermuda. A quick look around didn't find anything about the backers, management people or a need for F/Os:
https://www.aviationjobs.me/jobs/a32...l-jet-bermuda/
https://pilotcareercentre.com/Pilot-...muda/Coral-Jet