TLDR; there are a lot of features
Threaded group conversations

Talk about multiple topics at once without getting lost or overwhelmed.
One-on-one and group private conversations

Have private conversations with one or as many people as you need.
Persistence

We're always receiving messages for you, even when you're logged out.
History

Join a stream and see its history, so even new team members are never out of the loop.
Full-history search

Search is both snappy and smart, helping you look for text, people, and threads of conversation, with advanced search operators for fine-grained control.
Team presence and buddy list

See who is online at a glance.
Inline image, video, and tweet previews

Send a link and we'll automatically generate an inline preview.
Drag-and-drop file uploads

Drag a file into the compose box and we'll upload and preview it for you. Sharing and discussing work with teammates has never been easier.
@-notifications

Want someone's attention in a conversation? @-notify them and they'll be right over.
Stream-wide announcements

Use @all or @everyone to get the attention of everyone in a stream.
Emails for important missed messages

If you're missing important conversations when you're away from Zulip, we'll send you an email summary so you're always in the loop.
Desktop notifications

Configurable for private and stream messages.
Audible notifications

So you don't miss important messages even when your eyes are elsewhere.
Hotkeys

Type as efficiently as you do in your favorite text editor.
Emoji

Sometimes it's the simple things in life, like being able to give a :thumbsup: while chatting.
Code

Discuss code, even multi-line code, with ease, including syntax-highlighting.
Lightweight markup

Get bulleted lists, clickable links, and nicely-formatted e-mail pastes automatically.
Message editing

Don't worry, you can always fix that typo.
Invite-only streams

Enjoy the benefits of threaded conversations while controlling your audience and privacy.
Starred messages

Keep a todo list or keep track of interesting conversations.
Integrations

Get alerts and updates from your favorite services with off-the-shelf integrations for Trac, Nagios, GitHub, Jenkins, and more.
API

Want to roll your own notifications? We've got a dead-simple RESTful API and Python bindings that will make integrationsâboth sending and receivingâa snap!
Mobile apps

Check Zulip on the go with native iOS and Android apps.
Desktop apps

Prefer Zulip in its own window and rich, OS-level notifications? Enjoy Zulip on your desktop.