DOSBox is an emulator for old PCs running MS-DOS, focused on running classic PC games. Though it's under constant development, new versions are only officially released from time to time, with many updates inbetween only coming out as changes to the source code on SourceForge.
Here you can find compiled binaries of the original source, as well as an enhanced build and its source code, both created regularly soon after a new version is released on SourceForge. The enhanced build contains numerous patches with improvements that have been created by various users in the DOSBox forums on vogons.org. Because of that it's called "Enhanced Community Edition", ECE for short. The VOGONS community also is the place to go when you're looking for news, help or if you have a problem with or a question about DOSBox.
ECE, currently available for Windows and Linux, is maintained by YesterPlay and currently differs from normal DOSBox in the following features:
FYI: I currently can't provide updated Linux builds, because my VM stopped working all of a sudden. Again. I'll update the builds asap!