See more of JMAP in action from these providers:

JMAP software

Clients

JMAP Demo Webmail (JavaScript, MIT): a sophisticated demo webmail client to be used as a base for new projects. Default client for the proxy.
JMAP::Tester (Perl, Perl5): a JMAP client made for testing JMAP servers.
Cypht: lightweight Open Source webmail written in PHP and JavaScript.
Ltt.rs (Java, Apache): an email client for Android
Group-Office (Javascript): Open source groupware and collaboration platform
meli (Rust): terminal email client (GPLv3)

JMAP Proxy (Perl, MIT): a complete JMAP server implementation that uses any IMAP, CalDAV and CardDAV store as a backend. Also available as a hosted service at proxy.jmap.io.
Cyrus IMAP (C, BSD-style): A scalable enterprise-grade IMAP, CalDAV and CardDAV server. The 3.0 series is adding JMAP support, instructions to enable it are here.
Apache James (Java, Apache): Apache James, a.k.a. Java Apache Mail Enterprise Server is an open source mail server written entirely in Java. The 3.0 series is adding JMAP support.
Group-Office (PHP): Open source groupware and collaboration platform
atmail (golang, proprietary)

JMAP-JS (JavaScript, MIT): a full implementation of the JMAP mail, calendar and contacts model in JavaScript. It supports asynchronous local changes and is tolerant of network failure – actions will update the UI instantly, then synchronise changes back to the server when it can. It also has multi-level undo/redo support. Used by the demo webmail.
jmap-client (JavaScript ES6, MIT): a simple promise-based API to send requests to a JMAP server.
zend-jmap (PHP, New BSD): JMAP for Zend Framework
Java JMAP Library (Java 7, Apache): a low level jmap-client library as well as a higher level jmap-mua library.
melib (Rust): mail client library used in meli (GPLv3)

If you’re working on a project that uses JMAP, please open an issue or make a pull request on GitHub to update this page.