Kst (KDE4 Plotting Tool)

Kst is the fastest real-time large-dataset viewing and plotting tool available and has built-in data analysis functionality.
Kst is very user-friendly (both the community and the program itself!).
Kst contains many powerful built-in features and is expandable with plugins and extensions.
Kst is licensed under the GPL, and is as such freely available for anyone.
Note that KDE libraries are an optional dependency (i.e. you can run Kst without KDE,
but you get additional features when running on a platform with KDE).

Optional dependencies are: 
- gsl (a lot of very useful data analysis plugins are based) - RECOMMENDED
- netcdf (which provides support for files in the netCDF format)
- muParser (which is used in the general non-linear fitting plugin)
- GetData (which provides support for files in the Dirfile format)
- matio (which is used to read Matlab binary files)