Applications/Science
Appearance
Science
Plotting Data and Graphs
QtiPlot

QtiPlot analyzes and visualizes scientific data. Rocs

An interactive Graph Theory IDE for Students.
Data Manipulation
RKWard

A front-end for the R programming language designed for data manipulation
Simulations
KStars

A desktop planetarium from KDE, accurately representing the night sky from any location on the planet. Step

An interactive physical simulator which shows how a scene will evolve according to the laws of physics.
Information Systems
Kalzium

An application for viewing information about the elements in the periodic system. Marble

A powerful virtual globe and world map. It is able to use OpenStreetMaps. You can see it in action in this video