Absence - Employee vacation tracking system
productboard - Beautiful and powerful product management.
CWS TimeOut - CWS TimeOut is an online leave tracking software or absence management solution that can also be installed on the server.
Nifty - Manage projects, work, and communications in one place.
PTO Ninja - Slack app helping teams better manage time off
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.