Image from Firebox
More hardware than software but the Firebox USB Cassette Deck is a tape to mp3 converter that looks like a double tape deck that can be connected to the computer via USB connection. It can also be connected to an amplifier for tape-to-tape dubbing. It has two kinds of software one for copying. One is a copying wizard and the other one using Audacity for editing. According to the review, the software programs have some minor quirks but all in all, Firebox USB Cassette Deck is one of the better alternatives in cassette to mp3 converters out there.