TL;DR
I got fed up with having 11 chat tabs open all the time and made a userscript to fix it.
Screenshot
Description
A tiny widget that allows you to quickly chat in different Stack Exchange chatrooms from a single page.
Hover over any of the chatrooms shown on the right side of the page to pop up the small widget.
It will show a history of the last few messages from that chatroom (with full formatting, including oneboxes), the user who sent them, and a timestamp.
Type in the text field at the top to quickly send a message to that chatroom.
Hover over the username of any message shown in the widget to reply to, delete, or edit it.
The timestamp of any message shown also acts as a permalink.
The amount of unread messages will show up in
[brackets]next to the room names in the sidebar, and a total will be displayed in brackets in the title of the page (right next to the number in(parentheses)that shows the amount of unread messages in the current room, which stays intact).
Download / Code
Userscript can be found on GitHub (this post is just the README.md copy/pasted).