Presto provides a background Service which allows other applications to play MP3 and Ogg Vorbis files on your Android device at faster or slower speeds and/or faster or slower pitches. It does not provide a direct user interface to play audio files, but provides an API so that other developers can use speed and pitch adjustment in their apps. Developers must modify their app for Presto to be used while playing audio.
There's also a Presto Forum with ongoing discussion about Presto.
The Presto Client provides a nearly drop-in replacement for the android.media.MediaPlayer that will use the Presto service if available or gracefully degrade to use the android.media.MediaPlayer if it is not. The source is licensed under the Apache license.