FreeBu - Smart free/busy calendar sharing and meeting organizer.
Meekan - Connecting the world's calendars
Letsfind - Letsfind is a fast, easy-to-use, ad-free way to create online (meeting) polls.
FreeBusy Scheduling Assistant - Coordinate meetings 10x faster from Skype, Slack, Echo
FullCalendar - FullCalendar is an open-source JavaScript event calendar.
x.ai - x.ai is a tool to schedule meetings for you and your team.