Awesome Privacy

Free, secure and open source authenticator app for both iOS and Android. Supports creating encrypted backups and syncing between devices without the need for an account.

Free, secure and open source authenticator app for Android. Has a backup/ restore feature and a customisable UI with dark mode

Free and open-source two factor authentication app for Android. It features encrypted backups, icons, categories and a high level of customisation. It also has a Wear OS companion app

An easy-to-use, open-source two-factor authentication app designed specifically for iOS

Simple, native, open source 2-FA Client for iOS, which never connects to the internet - built by @mattrubin.me

Portable, encrypted desktop authenticator app for Microsoft Windows. With useful features, like hotkeys and some additional security tools, WinAuth is a great companion authenticator for desktop power-users. It's open source and well-established (since mid-2010)

Rust-based OTP authenticator. Has native With GNOME Shell integration. Also available through flathub.

Authenticator Extension is an in-browser One-Time Password (OTP) client, supports both Time-Based One-Time Password (TOTP, specified in RFC 6238) and HMAC-Based One-Time Password (HOTP, specified in RFC 4226).

Ente Auth is a free and open-source app which stores and generates TOTP tokens. It can be used with an online account to backup and sync your tokens across your devices (and access them via a web interface) in a secure, end-to-end encrypted fashion. It can also be used offline on a single device with no account necessary.