I just gave this a quick run. There aren't many options; however, it's very easy and quick to use. It can definitely suffice many use cases.
Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
FullCalendar - FullCalendar is an open-source JavaScript event calendar.
WhenIsGood - Plan the time to have your meeting or event by co-ordinating availability with all the particpants using this fuss-free online tool.
Letsfind - Letsfind is a fast, easy-to-use, ad-free way to create online (meeting) polls.
Framadate - Make your polls
CozyCal - Online appointment scheduling