I added some debugging statements to Reason that get turned on with the -d flag. These will output whenever a payload is added, whenever a heartbeat is felt, whenever payloads are delivered, and with the input/output of cell contents and executed code. This should do it:
yt serve -d
(There are also the -f and -o options.)
Also, I discovered that I added a Python 2.7-only feature without thinking, so Reason currently won't work with < 2.7.
This gets used in extdirect_repl.py on line 162 -- if somebody has a better idea how to handle this, it'd be great if we could simply replace it. Otherwise, we'll just mandate 2.7.
As it stands there are a couple big fish that need to be landed before this can be public: debugging and lots of use (although I am now using it all the time, almost exclusively, for analyzing my data), volume rendering widget (maybe something that looks like a less busy version of the widget I made with Traits in 2009? http://www.flickr.com/photos/matthewturk/4189749374/ ), phase plot / histogram of currently visible rectangular prism in the plot window widget, colorbar for plot window, and a few other things that are slipping my mind.
Anyway, because it's still in flux and a bit finicky in places, it's probably better not to publicize it too much. Once it's working better we can have a go at asking for beta testers and whatnot.