Cron - Cron Calendar.
Elevate - Elevate is an award-winning brain training tool designed to build communication and analytical skills.
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Peak - Peak is the automated way to keep track of what everyone is working on.
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
Brain Workshop - Brain Workshop is a open-source version of the dual n-back brain training exercise.