GalaxyNG includes an integrated forecaster/orders checker, a number of bug fixes, and changes the planet mix including more balanced galaxy generation than standard Galaxy. Bombing of systems reduces the industry and population to 25% of their previous value instead of sterlizing the planet. GalaxyNG is compatible with GalaxyTV, and through a set of options it is also possible to use the code to run standard Galaxy games.
Note that a bit more info would be appriciated here. I haven't played enough to do this justice.