SourceForge.net: Scribe
http://sourceforge.net/projects/scribeserver/
Scribe is a server for aggregating log data streamed in real time from a large number of servers. It is designed to be scalable, extensible without client-side modification, and robust to failure of the network or any specific machine.
Facebookのログ収集ソフトウェアProduct: Scribe - Facebook's Scalable Logging System | High Scalability