SORTING and MULTIPLY only allow Brainf**k. CRYPTO3 and SBSTR1 also allow only esoteric languages.
Those are the ones I remember, though there may be others.
If you feel up to the challenge, you might even choose to solve problems not specifically designed for Brainf**k in this wonderful language 
TEST has been solved in Brainf**k by several people, and a few more problems are also feasible.