Many tools exist that can help in the creation of an infiniteCD, tough none of them is specifically designed for this task. In addition, all of the existing tools require the mastering either of a programming langage, either of a specific and complex composition tool specialized in generative music, which, for the composer, means the collaboration with a musical assistant and/or a programmer.
Here are some pointers.
Koan from SSeyo : A commercial product designed for realtime generative and interactive music systems. Targetted towards websites. Based on a complex and powerful user interface. Fully featured on the sound side: audio, "vector-based", synthesizers and effects. Simple rule-based programming model. Was used by Brian Eno for the creation of his "generative music 1" pieces. Macintosh and Windows. Plugins for popular browsers.
Processing : general purpose multimedia programming environment. Contains various audio processing libraries. Opensource with a large user base. Java-based so available in authoring and playback mode on many OSes, including mobile phones.
SuperCollider : A real time audio synthesis programming language. Low level and very powerful. Can be used to create a generative music engine. Macintosh and Windows.
Max/MSP from Cycling'74 : Derived from the original Max program developped at Ircam. Commercial product with a huge user base. Fully featured on the sound side: audio, MIDI, synthesizers and effects. Powerful visual programming model, based on the 'patch' concept. More of a toolbox than a composition system, and not targetted to generative music but rather towards realtime sound effects. Macintosh and Windows.
Director from Macromedia : a powerful media-integration and programming environment. Fully featured on the programming side : a powerful object-oriented and interpreted langage. Quite weak on the sound side : 8 track sample mixer. Can be extended by specialised Xtras, like :
fluidXtra : an Xtra for Macromedia Director which integrates the fluidsynth software sound synthesizer into Director. Realtime sound effects, MIDI-compatible, internal sequencer, soundfont compatible.
Beatnik : a sound engine and editors around the XMF and RMF sound formats, designed to store sounds and MIDI and organise sound banks. The sound engine programmable through APIs. Editors on Windows. Sound engine on modbile devices (phones, etc..).
Pythoneon : music and audio generation langage based on the python langage. Not real time. Research.
jMax from Ircam (DISCONTINUED): jMax is an open source sound programming environment, derived from the original Max program developped at Ircam. Fully featured on the sound side: audio, MIDI, synthesizers and effects. Powerful visual programming model, based on the 'patch' concept. Works on Linux (Windows and Mac ports on the way). Compatible with Max/MSP. Open Source. Originally designed for interactive performances, this environment may be used to produce infinite CDs.