The first step to getting involved in development of Henry is to grab a copy of the SVN repository. At the moment, most active development is happening in the qt4 branch, which will probably become the main trunk in the near future.
To check out a working copy of the qt4 branch, use:
svn co https://henry.svn.sourceforge.net/svnroot/henry/branches/henry-qt
This will create the folder henry-qt, containing the current revision of the branch code. Our build system is cmake, so you'll need cmake 2.4 or higher, and qt 4.1 or higher (including the -dev packages if you're on a binary linux distro).
Code documentation at this point in development is somewhat sparse, but you're of course quite welcome to help remedy this if you feel like it. Otherwise, check out the current list of bugs and find something that interests you, and get hacking! We look forward to seeing your contributions in the near future.
One of our current major needs in the project is for quality documentation -- tutorials, examples of ways that Henry can be used in a school environment, anything at all. You don't need any specialised skills to help write documentation, and your contributions will be most welcome.
Non-developers can also get involved by helping to find bugs, and make suggestions about the future direction of the project. If you've found a bug, or would like to make a suggestion, head over to our sourceforge tracker and open a ticket, we'll get back to you as soon as we can.