Links
Here is a short presentation on topological data analysis.
An online LaTeX editor.
Tikzpicture is a tool to create fantastic graphics in LaTeX. (a minimal introduction, some examples)
Sage; a very useful mathematical software is to work with graphs.
Detexify is a nice tool where you can draw a symbol that you do not know its tex code.
MathB.in is a website for sharing mathematical text with others on the web.