I have uploaded the official 4.1 release of the Radiance source, together with binaries for Mac OS X:
http://radsite.lbl.gov/radiance/download.html
Unfortunately, I haven't figured out what I need to do for the radiance-online.org site, so that's stuck on 4.0 for the moment, though the HEAD is the same thing as 4.1 until it gets updated.
There have been a number of important features added in this release, excerpted from the release notes:
Modified dctimestep to accept sky vector and daylight coefficient matrix
or list of images to sum together, as suggested by Andy McNeil.
Created genBSDF script to generate BSDF in Windows XML format.
Added ability for rsensor to output ray origins and directions
rather than actually loading octree and computing sensor value.
Updated reflection model according to EGSR 2010 paper by David
Geisler-Moroder and Arne Duer.
Replaced C-shell version of falsecolor with Perl script written
by Axel Jacobs.
****** COMPATIBILITY CHANGE ********
Changed -sj (specular jitter) option to something called specular
sampling (-ss), which if set less than 1 has the same behavior as
the old -sj, but when set greater than 1, spawns multiple ray
samples from semi-specular surfaces.
Added BSDF data-driven material type with full sampling support.
Added BRDF calculations to genBSDF.
Added variable-resolution BSDF support in renderers and genBSDF.
Created pkgBSDF program to extract BSDF geometry and put it
together with surface description suitable for inclusion in
a Radiance scene.
Muted warning for "no light sources found" when there is at least
one glow object and interreflections are on (-ab > 0).
Checked in cross-platform cmake build system created by Bill Hoffman
of KitWare and sponsored by NREL. This includes a qt-based
driver for rvu, which is built in the new subdirectory src/qtrvu.
···
-------------
For full details, see:
http://radsite.lbl.gov/radiance/refer/Notes/ReleaseNotes.html
Best,
-Greg