Select the “Mail Plus” or “Proton Unlimited” paid plans for more features.
Proton Calendar
Official website proton.me/calendar
Our take
An end-to-end encrypted calendar where even event details and titles are hidden from the provider, which is rare and genuinely valuable, especially if you already live in the Proton ecosystem. The honest limits are practical: the best features sit behind a paid plan, and a fully encrypted calendar trades away some of the slick sharing and integration you get from Google. Pick it if you treat your schedule as sensitive data. Mainstream convenience seekers may find it more locked-down than they expect.
GitHub at a glance
ProtonMail/WebClients
Stars
5,478
+ 26 this week
Last commit
1d ago
healthy
License
GPL-3.0
Latest release
proton-authenticator@1.1.6
12d ago
Stars, last 10d
Listed in
Proton Calendar alternatives
Proton Calendar license, in plain English
GPL-3.0 Strong copyleft
Free to use and modify, but anything you distribute that is built on it must also be open under the same license.
Permits
- Commercial use
- Modification
- Distribution
- Patent use
- Private use
Requires
- Disclose source
- Same license
- State changes
- License and copyright notice
Does not provide
- Liability cover
- Warranty
Why it matters: Strong copyleft keeps every distributed version open. A vendor cannot fold this into a closed product and ship it without releasing their changes.
Plain-language summary of the project's license, not legal advice. Read the full text for the exact terms.