libevent is a cross platform library that abstracts out the different notification APIs (specifically, /dev/poll, kqueue(2), event ports, select(2), poll(2) and epoll(4)). It also supports triggering events due to timeouts or signals.

• Used by memcached
• Used by beanstalkd

• Your struct event objects need to remain valid after you've added them, so be careful about putting them on the stack.
• According to the libev developers, timer support in libevent is not as efficient as libev. See these benchmarks, and this list of other differences.

• libev, liboop

• The C10K problem - a collection of information about the different models for handling large numbers of connections.
• Comparison of libev and libevent