En su propia web lo definen como:

Gitter is a chat and networking platform that helps to manage, grow and connect communities through messaging, content and discovery.

Entre sus características está:

• Free without limits

  Enjoy free public and private communities with unlimited people, message history and integrations.

• Simple to create

  Simply create your community and start talking – no need to set up any invitation services.

• Markdown and KaTeX

  Format your messages just like with your other favorite developer tools.

• Out in the open

  Complete history archives(indexed by search engines) and sharable permalinks or use Sidecar to embed Gitter directly in your own site.