Please follow the appropiate instructions for your operating system
The binary (built) files can be found in the releases
Note: the releases have both 32-bit and 64-bit releases. If you don't know which one you should use, the 32-bit version should work on both 32-bit and 64-bit computers.
FOR MAC OS X USERS: there is no Mac OS X version as of now. Processing 2.2.1 seems to have a bug with exporting an application to OS X. This may be fixed in the future (if the Processing version is updated).
Installation note: executing the main executable file does not (or, at least should not) create any additional files apart from the data/level.gdat file (if it was deleted).
TL;DR: download the file you need, extract it and execute the executable file.
Windows
1 Download the matching file for your system (either 64-bit or 32-bit).
2 Extract the files from the .zip file (they should be in a folder named "GDE level editor")
3 Execute the "GDE_leveleditor.exe" file contained in the "GDE" folder
Linux
1 Download the matching file for your system (either 64-bit or 32-bit).
2 Extract the files from the .zip file (they should be in a folder named "GDE level editor").
3a Execute the "GDE_leveleditor" file contained in the "GDE" folder. If this fails, try step 3b before retrying.
3b Set the executable flag for the file (make the file executable). On Ubuntu and similar distributions, this can usually be done by right-clicking the "GDE" file, selecting "Properties" and setting the Execute option (under the "Rights" tab) to something like "Owner only".