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The MathOverflow question Open source mathematical software contains a list of programs that are useful to perform various computational tasks, such as computer algebra systems.

However, evaluating complicated formulas is not all that a professional mathematician needs to do. For instance, another important part of it is communicating results, producing papers and slides. There was a Mathoverflow question devoted specifically to tools for collaborative paper writing.

It would be useful to identify and gather on MO a list of areas of activities where research mathematicians can use software as part of their professional activity.

I think it would also be useful to gather on MO a list of software that does not strictly do computations, but is nevertheless useful to those who research and teach mathematics.

The first example that springs to mind is of course $\LaTeX$, but there is much more:

citation and literature management software, such as Jabref, Zotero, Mendeley

conference management software, such as Open Conference Systems (never actually used it, but it seems interesting)

reference tools such as the Online Encyclopedia of Integer Sequences and Plouffe's Inverter

Euclidean geometry software such as Geogebra

diff'ing and merging tools, such as latexdiff, kdiff3

specific LaTeX packages such as Beamer for presentations or several drawing packages (TikZ, Eukleides).

I find some of those real gems, and I'd like to find out more examples. So, the question is:

Can you provide (other) examples of programs that are useful to professional mathematicians in their job, while not being strictly speaking "software that does complicated computations"?

The question is a little broad and perhaps if there is much software relevant to a specific activity it will be wise to ask, based on input given to the question, a more specific question. Also please do not interpret this question too broadly (see discussion below).

Also check these MO questions: Tools for collaborative paper-writing (mainly regarding revision control software), Most helpful math resources on the web (mainly regarding online databases of something).