(Vixen 2.5 is used well by some, but is not as stable and has not been released. There are conversion utilities if you want to go from one version to the other.)
Why did the guy stop developing vixen further then what the software is now.
KC, the original author of Vixen, released a beta version of 2.5 in 2009, creating a small application that converted 2.1 files to 2.5.
Some people found problems with the 2.5 series and needed to switch back to 2.1, so KC created a "downverter," that brought 2.5-series files back to 2.1 format.
There are a large number of people who use 2.5 for their shows (me included). The reasons why some people can use 2.5 and others can't has never been fully explained, but the whole process gave KC pause.
But he did not stop developing Vixen; creating the software is his hobby and avocation and as with all hobbies, sometimes it's good to step away. He took 2010 off, leaving us with 2.1 and 2.5. If you can't run 2.5, you can run 2.1 and while KC never pulled the word "beta" off of 2.5, if you can use it, it is as stable as 2.1.
During his time away from Vixen, KC decided it needed to be rewritten from the ground up. Earlier this year he approached a couple of other software developers in the do-it-yourself Christmas community and they parceled out the project and a new 3.0 series of Vixen will be released soon -- though not in time for this Christmas season (an alpha may be released around the first of the year so that people can test it using displays already set up).
So: if you're adventurous or need dimming light curves on every channel, then go for Vixen 2.5. If you aren't feeling lucky and don't need dimming curves on every channel, then use Vixen 2.1.
HTH.
\dmc
PS: The new 3.0 series will still be free -- as in beer -- and it will be very modular. The APIs for the modules to plug into the core engine will be published and if people who develop modules want to make them Open Source and free (as in both beer and speech), that will be up to them.
