Teambit - Teambit is a team engagement and performance platform, that makes feedback a daily habit.
Calendarix - Calendarix is a powerful and easy to use web-based calendar that runs on PHP and MySQL.
Lattice Feedback - Give co-workers feedback in the moment
Cronofy - Unified Calendar API for developers
Manager Score - Benchmark your manager skills & get advice to improve
ApPHP Calendar - ApPHP Calendar is a PHP calendar script that may be easily integrated and used with various PHP projects, such as schedulers, event, etc.