160 bit hash function created in Europe by Hans Dobbertin, Antoon Bosselaers and Bart Preneel. It's similar in both strength and performance to more popular SHA-1. Because creation of RIPEMD-160 was more open than of SHA-1, one may expect that it's less likely that designers left some secret hole in algorithm. On the other hand, as it is less popular, less cryptographers tried to find hole in it, so it's more likely that some unplanned unknown hole exist in algorithm.
There also exist 128, 256 and 320 bit versions of this algorithm, called RIPEMD-128, RIPEMD-256 and RIPEMD-320 respectively. 256 and 320 bit versions only diminish chance of accidental collision, and don't increase security in any way as compared to, respectively, RIPEMD-128 and RIPEMD-160.
RIPEMD isn't restrained by any patents.