Data Converter is a tiny (34.4 KB download) tool which converts computer-related data (numbers, times, dates, IP addresses and more) from one format into something you can actually use.
Sounds dull, right? But for an example of how valuable this can be, launch REGEDIT and browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Migration. You'll probably see a value "IE Installed Date", which specifies its date/ time in the extremely unreadable REG_BINARY format (on our test PC, this was 86cde7a6cf66ce01). Totally useless, then - unless you have a copy of Data Converter.
To find out what this value really means, launch the program and select your conversion "From" ("FileTime [Hexadecimal QWord (Intel)]") and "To" ("Date & time") units. Now enter your value in "Input", click "Convert", and that's it - we found that 86cde7a6cf66ce01 actually means 18:15:28 on June 11th 2013 (and hopefully your date/ times will become similarly obvious).
There are plenty of other conversions on offer, too: DOS times, DOS dates, IP addresses, IP addresses ranges, hex DWORDS and QWORDs, often with Intel or Motorola variants. If you're not the technical type then it's easy to get lost.
Just the ability to run these simple date conversions is reason enough to download Data Converter, though. Grab a copy for your troubleshooting toolkit.