DataJoy is described as 'online Python and R editor for data analysis, statistics, numerical modelling and machine learning' and is an website in the Development category. There are nine alternatives to DataJoy, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and BSD. The best alternative is GNU Octave, which is both free and Open Source. Other great sites and apps similar to DataJoy are RStudio (Free, Open Source), Mathematica (Paid), Scilab (Free, Open Source) and IPython (Free, Open Source).
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.
IPython is an interactive shell for the Python programming language that offers enhanced introspection, additional shell syntax, syntax highlighting, tab completion and rich history. It is a component of the SciPy package.
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.