It turns .mym files into .csm files. .mym files are sort of the blueprints for themes, .csm files are the actual themes, but they're illegal to redistribute. .mym files are legal to share, so they are used to share themes, and then you use an app like ThemeMii to turn it into a .csm for installation.
edit: actually, its so much more than that. it can edit themes, make themes, download the necessary file from nus to make a csm, install themes to a nand dump (for use with sneek) and probably more too
Edited 1 time(s). Last edit at 02/16/2010 10:51AM by SifJar.