OpenRefine which used to be part of a Google project stream has become an almost irreplaceable tool for data cleansing and transformations. This is a part of activity regarded generally as data wrangling. One can clean messy data, transform data into various normalizations/denormalizations, parse data from various websites, merge data from various sources, and reconcile with Freebase (this has now been discontinued and work continues on Wikidata). However, the tool does have its many quirks and limitations. There are quite a few tools available as alternatives, most of which stem from research then end up becoming commercial products in their own right. Unfortunately, other open source options are only left as experimental and then slowly are made unavailable for public use. A few interesting free alternatives are listed below.
DataWrangler (commercialized into Trifacta)
Karma
Potluck
Exhibit
FusionTables
Many Eyes (discontinued)
DataCleaner
School of Data Online Resources
