libevent1 1.1a-2 (amd64 binary) in ubuntu gutsy

 The libevent API provides a mechanism to execute a callback function
 when a specific event occurs on a file descriptor or after a timeout
 has been reached.
 .
 libevent is meant to replace the asynchronous event loop found in
 event driven network servers. Currently, libevent supports kqueue(2)
 and select(2).
 .
  Homepage: http://www.monkey.org/~provos/libevent/