Simple Calendar Pro
Overview
Simple Calendar Pro is an offline-first scheduling and time-management application originally created by Tibor Kaputa as part of the open-source Simple Mobile Tools suite. Published under the GNU General Public License (GPL-3.0), the application was developed to provide an ad-free, privacy-respecting scheduling tool independent of proprietary cloud services and advertising SDKs. Following the acquisition of the Simple Mobile Tools brand by commercial publisher ZipoApps in late 2023, the open-source community created forks (such as Fossify Calendar), though the established Pro package remains widely recognized for its minimalist scheduling architecture.
The architecture of Simple Calendar Pro is centered around local data isolation. The application stores scheduling data within an encrypted or local SQLite database on the device, requiring no mandatory online account registration or external server handshakes. For users who require multi-device schedule coordination, the app interfaces with the Android Calendar Provider framework. This allows users to synchronize calendar data with platforms like Nextcloud, Google Calendar, and Microsoft Exchange via external CalDAV synchronization engines (such as DAVx5) without granting the calendar application direct network permissions.
The application provides extensive interface customization, allowing users to configure theme color palettes, widget transparency, font sizing, and visual density across Day, Week, Month, Year, and Agenda views. The scheduling engine handles complex recurring event rules, custom notification reminders, multi-tiered snooze parameters, and holiday calendar imports. Furthermore, the app ensures data portability by supporting direct iCalendar (.ics) file exports and imports, allowing users to backup or migrate schedules without proprietary lock-in.
By keeping all scheduling logic local to the device, Simple Calendar Pro ensures reliable performance, zero background battery consumption, and predictable operation without internet connectivity.
Pros & Cons
Complete Offline Privacy: Operates fully offline without network permissions, advertising SDKs, or background telemetry trackers.
Open-Source GPL Heritage: Built on open-source software principles, ensuring audited code security and clean system dependencies.
Open Data Interoperability: Supports full schedule backups, migrations, and restorations using standard iCalendar (.ics) files.
CalDAV and System Provider Integration: Interfaces with Android Calendar Provider to sync with self-hosted private clouds like Nextcloud via DAVx5.
Extensive Visual Customization: Provides detailed control over themes, accent colors, widget opacity, font scaling, and calendar views.
Minimal System Overhead: Lightweight installation package with zero idle background battery consumption.
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Commercial Acquisition Transition: The publisher transition in late 2023 has shifted active community development toward open-source forks like Fossify Calendar.
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No Natural Language Input: Event creation requires manual field and time configuration rather than parsing natural language text inputs.
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Requires Middleware for Cloud Sync: Synchronizing with cloud platforms requires installing third-party sync adapters rather than using direct in-app logins.
Download
Get it on Google Play 
Get it on App Store FAQs
Can Simple Calendar Pro function entirely without internet access?
Yes, the application stores all appointments, reminders, and calendar structures within a local SQLite database on the device's internal storage.
How can events be synchronized with a self-hosted Nextcloud server?
Users install an open-source CalDAV adapter (such as DAVx5) to sync their Nextcloud account with the Android Calendar Provider, which Simple Calendar Pro then reads and updates.
What is the relationship between Simple Calendar Pro and Fossify Calendar?
Following the acquisition of Simple Mobile Tools by a commercial entity in 2023, the open-source community created the Fossify Calendar fork to continue ad-free, open-source development.
How do users migrate their schedule data to a new device?
Users can export their complete calendar database as a standard .ics file via the settings menu and import it directly on the new device.
Does the app support shared meeting invitations?
While the app can parse basic .ics invite attachments, comprehensive enterprise meeting management and attendee tracking are better suited for dedicated enterprise calendar clients.
Hot Reviews
Summarized from Google Play reviews and community discussions.
Privacy-conscious users praise the app for its clean scheduling workspace, highlighting the lack of account requirements, tracking permissions, and background ads.
Reviews consistently praise the home screen widgets, commending the granular control over transparency, font sizes, and layout density for displaying daily agendas.
Feedback notes the change in publisher ownership, with long-time users discussing the transition and recommending the Fossify fork for continued open-source updates.