Cron - Cron Calendar.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Standard Notes - A safe place for your notes, thoughts, and life's work
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.