Just found this today. Works with gimp 2.8. I have some other batch tools such as xnConvert and irfanview, but they weren't preserving transparency with .png's correctly. BIMP just works. You can make processing chains and save them to files too, so you can put all your scripts in a nice tidy folder.
If Gimp is part of your workflow, this is a total godsend.
Develop games in your browser. Powerful, performant & highly capable.
Gimps always had a way to do batches.
You can even access it via a command prompt, or just make a script.
Both of which suck if you don't know syntax.
Didn't know that. Well, hey, if you are going to go with scripts, imagemagick anyone?