GnuPG (gpg)

GnuPG is a free cryptographic tool, that is havily used in the open source community. The GnuPG developers insist of implementing smartcard support from scratch, what makes a low smartcard variety.

gnupg-pkcs11-scd

gnupg-pkcs11-scd is a scdaemon clone that works with PKCS#11 smartcards. It is available via sourceforge here.