Sonic Architecture is Jan Jacob Hofmann. He seems to do a whole lot of composition in 2nd order ambisonics.
ambisonicbootlegs is a site with creative commons licensed ambisonic recordings and compositions.
Linux journal article on dirt cheap 3d spatial audio using Ville Pulkki’s VBAP and Mustajuuri.
California Nanosystems Institute’s new Allosphere project - worthy of a separate post really. Involves Stephen Travis Pope at UCSB, a thesis by Florian Hollerweger at IEM, supervised by Stephen Pope (UCSB), Alois Sontacchi and involving Robert Höldrich, both at IEM.
DXArts 3d audio lab at Univ. Washington
Maven 3D software for PC - not sure exactly what this does, but it sounds intriguing!
Shenonono suite of Pd patches for ambisonic composition.
IEM CubeMixer patches for Pd - also for ambisonic composition.
NASA AMES Research Center Spatial Auditory Displays Lab has developed SLAB - real-time virtual acoustic environment rendering system.
IEM Bin_Ambi is an ambisonic binaural renderer.
Also from IEM’s Sonenvir project, comes AmbIEM, which is an implementation of an Ambisonics rendering system for SuperCollider 3, largely developed by Thomas Musil.
Acousmodules offer a large variety of tools for multichannel composition.
This page on their site lists the features of a large range of multitrack and plugin host software packages that may be useful in multichannel composition from mono, stereo, 5.1 to many more channels. An interesting survey since I have recently become interested in exploring currently available audio processing environments that will support 5.1 and greater multichannel sound composition.