Zero (often stylized 0) is an open-source email client that aims to be a privacy-respecting alternative to Gmail. It connects to your existing inboxes and presents a fast, minimal interface focused on the basic email workflow — read, reply, archive — without ad tracking or marketing telemetry built into the experience.

The project is developed in public on GitHub under the Mail-0 organization and runs as a hosted web app at 0.email. It uses self-hostable infrastructure and is one of the more visible open-source email projects of the past year, with active changelog and contributor activity.