Calc is arbitrary precision arithmetic system that uses a C-like language. It's useful as a calculator, an algorithm prototype, and as a mathematical research tool. More importantly, calc provides a machine-independent means of computation. Calc comes with a rich set of builtin mathematical and programmatic functions.
GNU TeXmacs is a free wysiwyw (what you see is what you want) editing platform with special features for scientists. The software aims to provide a unified and user friendly framework for editing structured documents with different types of content: text, mathematics, graphics, interactive content. TeXmacs can also be used as an interface to many external systems for computer algebra, numerical analysis, and statistics. New presentation styles can be written by the user and new features can be added to the editor using Scheme.
Botan is a crypto library written in C++. It provides a variety of cryptographic algorithms, including common ones such as AES, MD5, SHA, HMAC, RSA, Diffie-Hellman, DSA, and ECDSA, as well as many others that are more obscure or specialized. It also offers SSL/TLS (client and server), X.509v3 certificates and CRLs, and PKCS #10 certificate requests. A message processing system that uses a filter/pipeline metaphor allows for many common cryptographic tasks to be completed with just a few lines of code. Assembly and SIMD optimizations for common CPUs offers speedups for critical algorithms like AES and SHA-1.
DOLFIN is the C++ interface of the FEniCS project for the Automation of Computational Mathematical Modeling (ACMM), providing a consistent PSE (Problem Solving Environment) for solving ordinary and partial differential equations. Key features include a simple, consistent and intuitive object-oriented API; automatic and efficient evaluation of variational forms through FFC; automatic and efficient assembly of linear systems; and support for general families of finite elements.
Ch is an embeddable C/C++ interpreter for cross-platform scripting, shell programming, 2D/3D plotting, numerical computing, and embedded scripting. It is the simplest solution to numerical computing and visualization in the domain of C/C++. It supports the ISO 1990 C Standard (C90), major features in C99 (complex numbers, variable length arrays or VLAs, type generic functions, long long data type, etc), classes in C++, and extensions to the C language like nested functions, string types, etc. It can be embedded in other applications and hardware and used as a scripting language. C/C++ code is interpreted directly with no compilation to intermediate code. It supports Linux, Windows, MacOS X, Solaris, HP-UX, and FreeBSD.
The Maximum Entropy Toolkit provides a set of tools and library for constructing maximum entropy (maxent) models in either Python or C++. It features conditional maximum entropy models, L-BFGS and GIS parameter estimation, Gaussian Prior smoothing, a C++ API, a Python extension module, a command line utility, and good documentation.
Libgvectors is a C++ library for visualizing three dimensional mathematical vectors, providing three fundamental classes for achieving its purpose. It makes as few assumptions as possible about the graphics library used to draw vectors on a screen and is not bound to any particular graphics library.