There are two versions of libev available, chose wisely:

libev-X.tar.gz

   The standalone library. Use this if you only need an event loop, and
   not extra baggage such as http and dns servers. Also use this if you
   want to embed libev into your own program without requiring an external
   dependency, or when you want to configure libev in a non-standard way.

Attic/libevent-X+libev-X.tar.gz

   This is the libevent library, with the core event parts replaced by
   libev. It should be functionally almost identical to libevent (but is
   not binary compatible). It is not updated as often, and not recommended
   (the libev tarball contains the libevent core emulation as well).
   libevent + libev is only available for very old versions of either
   library.

Full documentation for libev explaining use, portability and embedding
options can be found on its homepage at:

   http://libev.schmorp.de/

Direct link to the Changes file:

   http://cvs.schmorp.de/libev/Changes

Direct link to the current Documentation:

   http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod

For people automatically trying to download a specific version: the
current version and all older releases can be found in Attic/, while this
directory only contains the current release. So when you hardcode a URL,
hardcode one from Attic/.