Open Refine
Clean and transform data formats.
WTFcsv
Characterizes each column's data type to tell you what is going on with your .csv file.
Breve
Visualize messy data and find errors or gaps.
Gephi
Open-source visualization and exploration software for graphs and networks.
Palladio
Use .csv or spreadsheet to visualize data using maps, graphs, lists and galleries.
Tableau
Open data and explore it with Tableau Desktop Public Edition. Drag & Drop. Create stunning visualizations that are publicly available.