Toytomata
Work in Progress
Toytomata is an executable and a library that aim at helping with automata courses. The goal is to allow both students and teachers to enter language-related objects (automata, regular expressions, grammars, etc.) in a simple way and to run some usual operations on them. The main usage is to help check that different objects (and automaton and a grammar, for instance) recognise the same language, or to give a counter-example. This can be useful when grading, for instance, to compare a solution with the problem statement.
The API documentation is available here.
Installation 
The only way to install this software is currently manually, by downloading the sources, installing the dependencies and building the project.
See Also
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Automata Tutor v3, a website containing automatically-checked exercises on language-related objects.
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Automaton Simulator, a website which allows you to define automata using a graphical interface and to check whether they recognise words or not.
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CFG, an OCaml library for analysing and manipulating context-free grammars.
References
[Aho et al. 1983] Alfred V. Aho, John E. Hopcroft and Jeffrey D. Ullman. Data Structures and Algorithms. Addison-Wesley, 1983.
[Lange & Leiß 2009] Martin Lange and Hans Leiß. “To CNF or not to CNF? An Efficient Yet Presentable Version of the CYK Algorithm”. In Informatica Didactica, volume 8, 2009. http://ddi.cs.uni-potsdam.de/InformaticaDidactica/LangeLeiss2009.pdf
[Paull & Unger 1968] Marvin C. Paull and Stephen H. Unger. “Structural equivalence of context-free grammars”. In Journal of Computer and System Sciences, volume 2, issue 4, December 1968, pages 427-463. https://doi.org/10.1016/S0022-0000(68)80037-6