free chess GUI with adjustable strength

i am looking for a free chess graphical user interface that has adjustable playing strength. i already have fritz and CM 10 AND 11 im just looking for a free GUI with adjustable playing strength to play against. somebody help me out.

Try looking in Resources>Downloads.

The best GUI/engine combo for adjusting the strength is probably Shredder Classic.  Version 2 is available in Downloads (and can apparently be reinstalled) while 4 is available from the shredderchess site.  Rybka 2.2n2, Homer, Tornado and Ufim are free UCI engines that can be adjusted using the uci_elo parameter, and used in free GUIs such as Arena.  ChessAlex for UCI engines or Simple Chess for Winboard engines are GUIs that may be able to scale an engine that doesn't have uci_elo.  Chess Assistant 7 Light may be able to adjust strength as well, although it appears you can't set the time control when you do.  Most of these are available in Downloads.