JavaCard and MUSCLE (Score 2, Informative)

A previous poster mentioned the MUSCLE project. It provides lots of open-source software for talking to smartcards, primarily for cryptographic applications.

MUSCLE works with JavaCards . With these it is relateively easy to write your own applets that run on the card and do whatever you want.

Lots of vendors supply JavaCard-compliant cards. For example, SchlumbergerSema, iButton, and Gemplus.