JJ1 Level, by 
To anyone using this in the future: if editing the bmp files this tool extracts in Photoshop, Photoshop will save them with four trailing hex 00s at the end. I have no idea why it does this, but it alters the file size and causes everything to be offset by 1 pixel, causing some nasty streaking. If you want to use this tool and Photoshop, make your edits to the bmp, save it, and then open it in a hex editor like HxD and delete (not clear, but delete) the last four zeros from the file. You can then repack them to BLOCKS.000 or whatever without issue.
Other than that, very useful too, has been fun making some tweaks to the tilesets.
[Please rate Photoshop elsewhere, and limit your score to JJ1MOD here. Rating (4.5) removed. -Stijn]