Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.

Cron - Cron Calendar.

Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.

zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.

Daily Time Tracking - Daily shows what you have been working on and for how long. It creates accurate timesheets by asking what you are doing, so no more timers or switching tasks. Use its data to submit your hours, create invoices or simply increase your productivity.

Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.