The Ultimate Cyberware, in many *players'* opinions.  The Encephalon is an internal computer -- sort of a cross between a palm pilot and a backup brain.  It grants:

* A small IQ bonus, varying with the level purchased.

* The ability to automatically turn other cyberware on and off, and to easily coordinate data flows between them.

* A background thought process -- essentially a bonus equal to its level to all long term design and engineering problems.

* The ability to run other programs -- after all, it's a computer in your head.

There are many enhancements which require an Encephalon, or are only fully useful with one: [Math Coprocesser], [Cranial Memory], [Chip Jack], [Commlink] (internal radio), [Skillwires], [Cranial Encryptor], and [Cranial Cyberdeck].