Combined Chat is multistream chat in one window: Twitch, Kick, YouTube and Rumble together. It runs in a browser, so there is nothing to install and it works on any device.
Multistreaming splits your audience into separate rooms that cannot hear each other. The existing fixes are mostly plugins and desktop applications, which work for the person broadcasting and are useless to everyone watching. A viewer cannot install an OBS plugin.
Combined Chat is a website, which means a streamer can set it up and anyone can open it. Same tool, both sides of the stream.
This is a beta. It is free, it works, and things will change. Chat reading, the OBS overlay, login, sending messages and moderation are all live across Twitch and Kick, with YouTube and Rumble supported for reading. Subs, gifted subs, raids and Super Chats are picked out in the feed and pinned so they do not scroll away. Shareable links are live too: a streamer can hand their community one address that opens with their channels already connected.
More platforms. TikTok Live and SOOP are next, with X being worked out after that. Each new platform lands in the same feed and the same overlay, so nothing about the setup changes when one arrives.
Then the things one window makes possible that separate tabs never could. Moderating one person across every platform they are chatting on, in a single action. Alerts and text-to-speech for subs and donations that run in the browser with no plugin. Filters so a viewer can follow only the platforms or keywords they care about, and a nudge when they are mentioned. Sending to YouTube chat, which is possible through YouTube's official API and is being worked on.
Some of the earlier items on this list have already landed: several channels on the same platform at once, and live viewer counts on every channel. The setup guide covers how they work, and the comparison page is honest about where other tools still do more.