I am the lead developer and main contributor of the Grapher Android application, whose source code is available under a free license at github.com/drange/Grapher. Please have a look at it, and I am very happy for any feedback you may have.
This app is a pet project for drawing graphs, exporting to tikz and metapost (and soon pictures), running algorithms on graphs, etc. It started as a simple way to make TikZ code by drawing a graph, but as time passed, we implemented algorithms on these drawn graphs, especially NP-hard ones.
We use this as some programming projects in algorithms for students, like
Steiner tree computation in FPT time Minimum fill-in computation in FPT time Chromatic number and coloring in fast exponential time Interval representation view (ongoing) Odd cycle transversal in 3k time Maximal matching (paths, trees and flowers) (ongoing)
More other stuff
The collaboration graph of my research group with present and former members.
The collaboration graph of my department.