Free and secure calls and messages to anyone, anywhere.
Run Android Messages as a desktop app, a la iMessage
FOSS messaging and emailing app that combines common web applications into one
Copies the text messages off an iPhone into a CSV file you keep, on your own PC. Free, no upload.
Google Messages for Web on Windows. Runs "Messages for web" in a native Windows application. Close to system tray. Ctrl+Alt+M to show window.