Simply put: Yubutils are a set of programs that allow access directly to YubNub directly from your computer (OS X, Linux or Windows).

The yubutils project is a grouped project that houses three main downloads.
1. yubController - a GUI front end for yubnub.
2. yncs - a text interface for yubnub and pipe developers (included in the yublib downloads).
3. yublib - the core of yubutils front ends. Python library to interface with yubnub