atracdenc Open source ATRAC1 and ATRAC3 Encoder. Not known for being the highest quality encoder.

Exact Audio Copy by Codemasters (for GTA)

Open MG - Used by Sonic Stage Archive.org repo

RealJukebox Basic

RealProducer Basic

Simple Burner 2.0.05.25150 (Jan 15, 2005)

Sony .acm codec - integrates with the Windows Audio Compression Manager and encodes to ATRAC3 files wrapped in the WAV container, allowing bitrates of 66, 105 and 132kbps. Keep in mind this is quite old code and probably does not reflect the best quality ATRAC3 can provide.

Sound Forge (Built-in since version 9, but you can add the plug-in to version 6 onwards)

SONY Cinescore 1.0

RealJukebox Plus

RealProducer 8 Plus

Sonic Studio's N-code plugin for professionals

ATRAC Codec Plugin for Sony Media Software (Windows only)

SCEI ATRAC3plus and ATRAC9 Codec tools