Matrix: Protocol (like SMTP/IMAP)

Element: The most popular client (like Thunderbird)

Element X: Rewrite of Element based on Rust and native UI components

Synapse: Most popular Matrix server (like Dovecot)

Element Call: Video/Audio conferencing (like Jitsi)

Element Server Suite (ESS): Paid SaaS solution that wraps all of the mentioned components into a simple turnkey solution.