FreeOTP works with many of the great online services you already use, including Google, Facebook, Evernote, GitHub and many more! FreeOTP also may work for your private corporate security if they implement the standardized TOTP or HOTP protocols. This includes great enterprise solutions like FreeIPA.
FreeOTP is open source and free software! Licensed under the Apache 2.0 license, you can obtain the source code for FreeOTP at https://fedorahosted.org/freeotp for review or modification. Contributions are welcome!