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Proton
Empowering you to choose a better internet where privacy is the default. Protect yourself online with Proton Mail, Proton VPN, Proton Calendar, Proton Drive. Proton Pass and SimpleLogin.
Proton Mail is the world's largest secure email provider. Swiss, end-to-end encrypted, private, and free.
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Proton Calendar is the world's first end-to-end encrypted calendar that allows you to keep your life private.
Proton Drive is a free end-to-end encrypted cloud storage that allows you to securely backup and share your files. It's open source, publicly audited, and Swiss-based.
Proton Pass Proton Pass is a free and open-source password manager which brings a higher level of security with rigorous end-to-end encryption of all data (including usernames, URLs, notes, and more) and email alias support.
SimpleLogin lets you send and receive emails anonymously via easily-generated unique email aliases.
If you give the lightweight os DietPi a shot, Proton VPN works via their DietPi-VPN tool right off the bat. You just need the IKEv2 username/password combo from your Proton VPN settings. It will always connect to the same server you specify in the settings as well. I believe OpenVPN should work the same but can't confirm. I'd definitely recommend DietPi if you're looking to self-host any services - especially on a 3B. It's super lightweight and has a tonne of graphical config tools that makes setup a piece of cake.
I can't install any other OS on it right now so I'll try openvpn