DAVx⁵

CalDAV/CardDAV Synchronisation and ClientGPL-3.0-only

KashCal

All your calendars in one app. iCloud, CalDAV, device, ICS. Private.Apache-2.0

Infomaniak kSync

Automatically sync your contacts and calendarsGPL-3.0-only

Cfait

Powerful, fast and elegant TODO / task manager. (CalDAV and local)GPL-3.0-only

Tasks.org: Open-source To-Do Lists & Reminders

Private, ad-free task lists! Optional sync with Google Tasks, CalDAV or EteSync!GPL-3.0-only

jtx Board journals|notes|tasks

Keep track of journals, notes & tasks - iCalendar compliant and syncable with yoGPL-3.0-only

Linwood Flow Nightly

Feature rich event, group and time management systemAGPL-3.0-only

Gridlink Mail

A fast, private JMAP and IMAP email client. No ads, no tracking, no Google.GPL-3.0-only

Agenda Tech

Private offline calendar: encrypted, zero network, encrypted backups.Apache-2.0

OpenTasks

Keep track of your list of goalsApache-2.0