wig-solver 

A chrome extension which adds functionality to WhenIsGood to simplify office-hour scheduling.

SmallCategories 

A database listing all categories with very few (currently, ≤7) morphisms, up to isomorphism. As far as I know, SmallCategories is the only resource of its kind – if you happen to know otherwise, please contact me!

pycatlib 

A very small python library for computing with finite categories. There is more to come in this direction!

Math Data Wizard 

A very small web app for moving lists/matrices/etc. between different math software systems (Sage, Mathematica, etc.)

Created with Thomas Brazelton

I am also a founding member and editor of MathBases.org, a database of mathematical databases.