tl;dr: Tether is a new MIT-licensed tool that brings Apple Continuity-like features to Linux with an iPhone, including iMessage/SMS, notifications, contact sync, file transfer, clipboard sync, and OTP autofill (via browser/mail extensions for Zen and Betterbird). The iMessage/SMS breakthrough came from a clean-room C++ reimplementation inspired by ancs4linux and BlueFerry's protocol documentation, communicating over Bluetooth with mTLS security. The author positions it as an alternative to KDE Connect for iPhone users and is seeking contributions, especially for broader mail client support.