DAVx⁵ – CalDAV CardDAV WebDAV

Kanbani is a free kanban task manager with offline support, cross-device sync, Excel/Trello export, and a Timeline view to convert the board into a calendar. It runs without ads or telemetry, but has UI/UX and documentation issues.

Kartha is your all-in-one productivity OS — tasks, notes, calendar, routines, habits, and more, all connected in one system.

Microsoft Outlook is a full-featured email client with support for multiple services, smart filtering, calendar, and Microsoft 365 integration, but suffers from notification synchronization issues and periodic access failures.

ColorNote is a simple notes app for creating notes, to-do lists and reminders with color organization, device synchronization and cloud backup.

Multifunctional email application with calendar, cloud storage and notes integration, supporting multiple mail accounts with an AI assistant for email summarization.

HabitBull is a habit tracker with flexible reminders, progress charts, and cross-device synchronization. Primarily operates in English and has issues with registration and outdated interface.

Shift work scheduling app with automatic alarms, income tracking, and cross-device synchronization, operating fully offline without registration.

Tasks.org is an open-source task management application with support for nested subtasks, synchronization (Google Tasks, CalDAV, Nextcloud, EteSync), reminders, and widgets, with partial functionality available in the free version and paid synchronization for certain services.