via http://groups.google.com/group/twitter-development-talk/browse_thread/thread/6f24e47cca5b68f6

We've successfully moved to the OpenFire Jabber server, and now have far more visibility into our XMPP services overall.

だから20req/hr制限なのかしら。
それにしても、早くtrackを復活させて欲しいです。
http://twitter.com/account/rate_limit_status.xml

OpenFireとは

Javaで書かれているそうです。twitterが以前使っていたejabberdはErlang。そしてあんまり情報がない...

Openfire (formerly Wildfire) is a real time collaboration (RTC) server dual-licensed under the Open Source GPL and commercially. It uses the only widely adopted open protocol for instant messaging, XMPP (also called Jabber). Openfire is incredibly easy to setup and administer, but offers rock-solid security and performance.
http://www.igniterealtime.org/projects/openfire/index.jsp

twitterが以前使っていたJabberServer：ejabberd

http://www.jabber.org/servers/ejabberd
http://www.atmarkit.co.jp/news/200704/27/erlang.html

Refs

http://www.jabber.org/servers
http://www.jabber.org/servers/openfire