MathJournal is described as 'interactive program for the Tablet PC that provides a natural and intuitive environment for solving mathematical and engineering problems' and is an app in the Education & Reference category. There are more than 25 alternatives to MathJournal for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and Android. The best alternative is Wolfram Alpha, which is free. Other great apps like MathJournal are GNU Octave (Free, Open Source), R (programming language) (Free, Open Source), MATLAB (Paid) and Mathematica (Paid).
Wolfram Alpha is a "Computational Knowledge Engine" - different from a search engine, it answers factual queries directly by computing the answer from structured data, rather than providing a list of documents or web pages that might contain the answer.
Octave is a computer program for performing numerical computations which is mostly compatible with MATLAB. It is part of the GNU Project. It is free software under the terms of the GNU General Public License.
MATLAB is a numerical computing environment and programming language. Maintained by The MathWorks, MATLAB allows easy matrix manipulation, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs in other languages.
SageMath is a free open-source mathematics software system licensed under the GPL. It builds on top of many existing open-source packages: NumPy, SciPy, matplotlib, Sympy, Maxima, GAP, FLINT, R and many more.
Spyder (previously known as Pydee) is a free open-source Python development environment providing MATLAB-like features in a simple and light-weighted software, available for Windows XP/Vista/7, GNU/Linux and Mac OS X.
Maxima is a system for the manipulation of symbolic and numerical expressions, including differentiation, integration, Taylor series, Laplace transforms, ordinary differential equations, systems of linear equations, polynomials, and sets, lists, vectors, matrices, and tensors.
wxMaxima is a document based interface for the computer algebra system Maxima. wxMaxima uses wxWidgets and runs natively on Windows, X11 and Mac OS X. wxMaxima provides menus and dialogs for many common maxima commands, autocompletion, inline plots and simple animations.