Memcached is an open source high performance distributed memory object caching system. It is one of the most widely used cache mechanism used by some of the biggest websites like Wordpress.com and LiveJournal.com. It is also used by VBulletin software, for faster performance, that is one of the best software for Forums. Its easy to install and there are so many client programs available on Internet in different languages.
Memcached is a memory based caching mechanism and build using C language. To install memcached server on Mac OS or Linux we need C library. Here I am assuming that C library is already present in the system. If its not, then you can download C compiler and install it or install XCode that installs gcc compiler with it.