Recently there has been a lot of interest in MR. One of the important reasons is that it makes writing parallel applications, especially those that have to deal with huge amount of data distributed over unreliable computers, very easy.
Yahoo! is currently running a Hadoop cluster of over 1000 nodes, and they are doing pretty interesting stuff with it.
Although Hadoop has emerged as the leading open source implementation there are others worth mentioning:
- The QT Concurrent package supports MR. I am not sure if it has support for distributed operation though.
- There is an MR implementation available for Ruby called Skynet(don't know why they chose this name) as well, like every other thing that Ruby has, this also makes writing MR code ridiculously easy.