I'm the designer and primary developer of MegaTunix. Originally designed to support the MegaSquirt and it's derivatives. Since VEMS has a MegaTune compatibility mode MegaTunix can talk to it just as well. The current MegaTunix work is done primarily in CVS, and is the place to be to see what is going one.
The major new work being done on MegaTunix is to allow the Gui to be dynamically generate-able, an idea I got from Marcell. It unfortunately took me about a year to figure out how to do it... But, as of now, all ECU related Gui tabs are designed with the Glade GUI Designer, http://glade.gnome.org/ I'd suggest using the 2.0 version as 2.6 is still a bit buggy, and I use 2.0.1 to design the GUI and libglade-2.4 to parse it and load it on demand. Since Glade isn't the end-all do-all application, I had to write some other code that sets the numerous attributes on widgets and thus with each .glade file is what's known as a .datamap file. (An ascii text file that maps widget attributes to widgets named in the glade file). This allows for very good flexibility and user generation/redesign of parts of the gui in a fairly simple manner.