I build and share these tools:
Display and manipulate a breakdown structure of your JIRA Scrum project - even offline and only eventually connected to your JIRA system.
A virtual whiteboard to be shared by multiple persons at the same time. Users will be anonymous - so no one needs to sign in.
A Sorted Map and a Sorted Set, implemented as a binary tree.
Make the header of your web pages dynamic.
Draw SVG Cumulative Flow Diagrams and predict the anticipated completion of work.
Draw SVG Stacked Area Diagrams with a day-based x-axis.
File your workout routines and get a nice graphical overview of your achievements and improvements.