Superuser by koush

An app to allow or forbid apps' requests to run as root. Note that this app doesn't include the su binary, so your device must already be rooted.

You must already have root for this to work, because it leverages the existing su and Superuser app to install itself. However, if you know what you are doing you can use this apk as a su/Superuser substitute if you are gaining an initial root. Once the install is completed you can disable or remove the old app.

For full details and additional technical information, see this application's page on the F-Droid wiki.