Create chat room with feature parity to highly traffic'd Q&A site

I am looking for a chat room application that has feature parity with a highly traffic'd IT Q&A site. A high level overview of my requirements is listed below. - Ability to star messages and appear on transcript wall with a daily maximium per user - Multi room; Users can be in multiple rooms - Private rooms (passworded) - Users can create own rooms - Ability to favorite a room - Ability to rejoin all favorite rooms - Persistent chat history with archives created every 24h - Ability to flag messages - Reply to specific message - Notify user; highlight where they are notified - Steam OpenID Integration - Onebox for images, youtube videos, etc. with easy interface to build new oneboxable content - Notification when messages are posted (ie page title change) - Notification with sound when message directly to user is send (sound must be toggleable) - Suggested user names when @mentioning them - Link to specific messages (message has it's own link); when linked the message is highlighted - Searchable - Limited Markdown of messages: Bold, italics, underline, strikeout, links in this format: [text to show]([login to view URL]), code block - Integration with Imgur to provide upload place for pictures - Ability to edit messages for 5 minutes after posting OR until a new message is posted - Posting history for all messages is saved - Indication of edit is shown - Room owners - person who created room AND system admin(s) - Moderator - Can remove messages, can remove/ban/mute/unmute/unban user by Steam Profile ID, gets notified of flags for room(s) they are moderator of - System Admin - Can set system settings - Permissions: - Who has access: Whitelist by username AND/OR user group (default is everyone can enter) - Who can talk: Whitelist by username AND/OR usergroup (default is everyone can talk) - User can have access to the room by not have access to talk (read only) - User can have access to room by group, can have access to talk by username - Freeze room - No more talking by anyone; basically used to close a room - Room will freeze automatically if not used in X days (configurable at system level) - Delete room - Archives automatically; removes room from list of available rooms; disconnects all users in the room - Add/remove RSS feed - URLs that will be periodically queried and new messages will be posted to the room - Usable API - Should contain an API to interact with system - Create message - Star/Flag message / Unstar/Unflag message - Read messages in room - System itself should use this API (to confirm it works) - System should be able to react to certain events per room and API should be able to list what events are available: - Messge sent - Broadcast Message received - Joined - Left - @notified message - On flag - On unflag - On star - On unstar - Ability to add new events easily - UI - UI must be easily changed via CSS/Template modifications - Security; user must be a validated user (via Steam OpenID) - Technical requirements: - Must run in browser on standard port 80 or 443 (if using SSL) - Chat messages must persist through log in and log out of various users - Each chat message must have unique link - Archiving can be a scheduled task and should not clear existing chat rooms or be indicated in UI - Translation: If a user logs in to a chatroom 3 minutes after an archive occurs, the previous chat messages must still display - Users must be able to receive unique notifications for each room they are in - Users can have different permissions for different rooms - Minimal number of 'things' to install/maintain; would be best if it can be front end package (python/nodejs/php) and backend (mysql/postgres/redis) only, but not opposed to required other things - Functional on mobile devices (phone and tablet sized) - System must be able to run without root/administrator rights A more complete listing of features will be provided to winner (limited here due to space limitations)