Yubico PIV Tool
This is a command line tool to interact with the PIV applet on a YubiKey NEO. Among other functions it supports, generating keys on device, importing keys and certificates and creating certificate requests.
The YubiKey NEO supports the Privilege and Identification Card (PIV) interface specified in NIST SP 800-73 document "Cryptographic Algorithms and Key Sizes for PIV". This enables you to perform RSA or ECC sign/decrypt operations using a private key stored on the smartcard, through common interfaces like PKCS#11.