WAV-PRG is a program able to create a .TAP file or Commodore 64 tape from a C64 emulator file (.PRG, .P00, .T64), create a clean .TAP file from a .TAP or .WAV file, and create emulator files (.PRG, .P00, .T64) from a Commodore 64 tape. The latter can only be done if the tape is in a format supported by an existing plug-in. Audiotap is a program for conversion between .TAP files and Commodore 64 tapes. Audiotap can read/write WAV files containing the sampled sound of a tape, and can also record tapes from the sound card and play sound to the sound card.
Both program can read tapes from WAV samples, or directly from sound card input. They can create WAV files, which can be later recorded to tapes, or play sound to sound card, so tapes can be recorded directly. Because of this, they do not require custom-built cables, just plain audio cables connecting the sound card and a normal audio tape player/recorder.
Both programs are available for Windows and Linux. They are distributed under the GNU General Public License so they can be downloaded and used for free.