If you want people to be able to contribute to your code and use it as a freely cooperating community without legal problems, I would suggest at least two things:
(1) Add a licence to the package, e.g. see gnu.org/licenses/licenses.html
for a discussion of some of the various possible free (GPL compatible or GPL non-compatible) and non-free licences, e.g. GPL would be the obvious licence, but it's something to discuss among participants and decide on. If you say nothing
about licensing, that does not
make it public domain. By default, the authors hold a conventional copyright on their contributions. In principle, nobody is allowed to redistribute original or improved versions of icosmo unless they specifically contact all of you (the authors) and get your agreement every time. Just because it's on the web doesn't make it "public domain".
(2) You've presented your package to be used with a non-free
software package called "IDL". This, for example, makes it potentially illegal (at least in the USA, maybe not in the EU) for people to write their own programs which read or write IDL "save/restore" files, at least according to the wikipedia entry on IDL
: IDL Save/Restore files embody unpublished proprietary information about the IDL program. Reverse engineering of this file is therefore forbidden under the terms of the IDL End User License Agreement. ... Non-RSI supplied software that reads or writes files in the IDL Save/Restore must have a license from Research Systems explicitly granting the right to do so. ...
If you want to free people from this sort of constraint and encourage normal scientific collaboration, I would suggest that you test your program using the GNU Data Language (GDL)
. GDL is protected under the GPL, so anybody can essentially do just about anything with it they like (use it, modify it, redistribute it, distribute modified copies) on the condition that they give the same freedoms to other users, i.e. they keep the same licence. My guess is that it wouldn't take much effort to check, and in the long term, there's more of a chance that this would become a community tool.
The Source code for iCosmo is publicly available on the web...
As it stands at the moment, a more precise description is that your package is publicly available but non-free
and recommends the use of a non-free programming package