If a software company, startup or otherwise, asks you to basically build half their product for them before they'll even give you a phone interview, then demands that your first 3 months will be an unpaid internship for this wild & crazy reason, run away.
https://www.reddit.com/r/cscareerquestions/comments/78rhz7/this_startup_asked_me_to_do_a_project_for_an/