OpenSC implements PKCS#11 API so it can be used as plugin in applications
like firefox, thunderbird or plain mozilla. OpenSSH has support for smart cards
using libopensc, OpenS/Wan can use OpenSC and many other applications
can use smart cards as well - using OpenSC.

We ship OpenSC as open source software under LGPL license. It consists
of our library libopensc with new interface, of opensc-pkcs11.so module
implementing the PKCS#11 standard interface, a collection of tools
for using smart cards in many different ways.

OpenSC has a number of sister projects including: OpenCT, a project for
open source drivers for smart cards reader, including its own middleware.
Libp11, a library sits on top of PKCS#11 API and aims to be easier to use.
Engine_pkcs11, an engine module for openssl, so openssl based application
can use a smart card for crypto with no or little changes. Pam_p11 is a very
simple pam module for smart card based authentication. Pam PKCS#11
is a full featured authentication module for smart card based authentication.