WaveSurfer is an open source tool for sound visualization and manipulation. Typical applications are speech / sound analysis and sound annotation / transcription. WaveSurfer may be extended by plug-ins as well as embedded in other applications.
Features:

• Customizable – users can create their own configurations. Localization support.
• Extensible – new functionality can be added through a plugin architecture.
• Embeddable – WaveSurfer can be used as a widget in custom applications.
• Transcription file formats – reads, and writes HTK (and MLF), TIMIT, ESPS/Waves+, and Phondat. Support for encodings and Unicode.
• Multi-platform – Linux, OSX & Windows.

sourceforge.net/projects/wavesurfer
en.wikipedia.org/wiki/WaveSurfer