Before a new release the Emacs maintainers make a “pretest” release of the EmacsDevelopmentSources. There are binary packages for pretests available to Windows users, but otherwise its just a source package – see BuildingEmacs.
I tested this on 2014-06-29 (Windows 8, 64-bit) and it seems to work well, with image support and all. – MaDa
I tested this on 2014-06-29 (Windows 8, 64-bit) and it seems to work well.
These binaries are packaged as given by “make install”, so they don’t bundle binaries of optional external libraries. See  for instructions on setting up a runtime environment with those libraries.
This is a trunk release updated from time to time. Compiled with MSYS2/Gcc 4.9, optimized, with all supported libraries.
See also EmacsReleaseDates.