Praat is an application with which phoneticians can analyze, synthesize, and manipulate speech and create high-quality pictures for their articles and doctoral theses.
The source code may be downloaded here.

What’s new in this version:

Version 5.0.13:

• Corrected drawing of histograms.
• TextGrid window: selected part of the TextGrid can be extracted and saved.
• TextGrid: more complete conversion between backslash trigraphs and Unicode.
• Formulas: sinc function.

Website
Download Praat