While using D3 for the first time, I found myself frustrated keeping track of how the number and date format specifiers operated. So, I built a tiny tool to test out many specifiers at one time.
Evidently I wasn't the only one who could use a little help with formatting.
This bl.ock is now Google's "one box" search result for a search on "d3 number formatting."
In his OpenVisConf presentation on Tiny Tools, Adam Pearce mentioned this tool to make the point that "you don't have to be afraid of making [tiny tools]."
It was a nice surprise to find that first, and simplest, D3 bl.ock could end up being so useful.