RIPEMD is a cryptographic hash based upon MD4. It's been shown to have weaknesses and has been replaced by RIPEMD-128 and RIPMD-160. These are cryptographic hash functions designed by Hans Dobbertin, Antoon Bosselaers, and Bart Preneel.
The name comes from the project they were designed for: the EU project "RACE Integrity Primitives Evaluation" (RIPE), 1988-1992.
RIPEMD-160 produces a hash of the same length as SHA1 but is slightly slower. RIPEMD-128 has been designed as a drop-in replacement for MD4/MD5 whilst avoiding some of the weaknesses shown for these two algorithms. (These are possible hash collisions.) It is about half the speed of MD5.