irrKlang is a high level 2D and 3D cross platform sound engine and audio library that plays WAV, MP3, OGG, MOD, XM, IT, S3M, and other file formats. It can be used by C++ and all .NET languages (C#, Visual Basic.NET, etc.). It has all of the features common to low-level audio libraries as well as lots of useful features like a sophisticated streaming engine, extendable audio reading, single and multi-threading modes, 3D audio emulation for low-end hardware, a plugin system, multiple rolloff models, sound effects, and more. All of these can be accessed via an extremely simple API using an object oriented design.
JackMixDesk is based on JackMiniMix and is a general purpose mixer for the Jack Audio Connection Kit. It has an OSC-based control interface, and a configurable number of mono/stereo inputs and pre/post sends/outputs that can be controlled by sending it OSC messages. There is LASH support and an XML config file.
bcr beats is a beat slicer that lets you cut up and play with an audio sample: you can trigger slices and loops with MIDI or the mouse and keyboard, set pan, volume, and sample rate values, and generally have lots of fun. The interface is based on the Behringer BCR2000 MIDI controller, which means lots of knobs. It can be used with or without a controller.
BpmDj is a program that can be used by a DJ. It plays MP3 and Ogg files. It has a fully automatic BPM counter. It can determine the sound color. It has a full fledged Qt based interface. It will help you manage a large amount of songs. It can help in creating playlists and has proven to be very robust. The program also allows offline automatic mixing and contains a wavelet based beat graph analyzer to visualize audio tracks.
As a plugin API, Frei0r's main emphasis is on simplicity, to round up the most common video effects into simple filters, sources, and mixers that can be controlled by parameters. Frei0r plugins can be shared by many host applications, avoiding duplicate efforts by different projects. Frei0r is not meant as a competing standard to more ambitious efforts trying to satisfy the needs of many different applications and more complex effects, as it doesn't provides things like an extensive parameter mechanism or event handling.
JackMaster is a master-mixer for jackd that (unlike jackeq) works like a real console, with a simple fader -> subgroup -> master routing. Unlike jackmix, it has faders instead of knobs. It features low CPU usage, optional session management with LASH, and optional fader automation with the ALSA sequencer.