CCMATH is a mathematics library, coded in C, that contains functions for linear algebra, numerical integration, geometry and trigonometry, curve fitting, roots and optimization, Fourier analysis, simulation generation, statistics, special functions, sorts and searches, time series models, complex arithmetic, and high precision computations.
Genius is an arbitrary precision integer and multiple precision floating point calculator. It includes its own programming language similar in some aspects to C, bc, or Pascal. It can deal with rational numbers and complex numbers. It has matrix support as well. It uses the gmp library so it is very fast for calculations of large numbers. It has a command line and a GNOME interface. The GNOME interface supports plotting functions and 3D surfaces.
GtkMathView is a GTK widget for rendering MathML documents. It is meant to be a standalone, light-weight component and not a full browser. GTK applications can use the widget as a window for displaying mathematical formulas and doing simple interactions. Among other features, GtkMathView includes support for breaking long mathematical expressions, rendering of stretchy operators, and provides a customizable support for additional fonts.
KSEG is a program for exploring Euclidean geometry, similar to Geometer's Sketchpad. It features points, lines, transformations, measurements, calculations, simple editable recursive Constructions (similar to macros), adaptively sampled loci, and selection groups. Several languages are supported. KSEG is very fast, stable, and has an efficient and consistent UI. It uses Qt and does not require KDE.