UnitStar unit converter
Note: UnitStar is no longer being updated. The last version was 1.11, released in December 1998.
UnitStar is a unit conversion program for Windows. It comes with a comprehensive database of measurement units, background information about each unit, and an open file format that lets you define your own custom units. UnitStar adopters come from all sorts of technical professions: researchers at federal labs, professors at universities, engineers with oil companies, and many more.
UnitStar was a Finalist in the 1998 Ziff-Davis Shareware Awards, awarded by PC Magazine.
UnitStar is free to try for 30 days, and costs $8 to buy. Trial version is fully-functional and has all units, but has a nag screen and no unit description data. Requires Windows 3.1 or above. Works on 32-bit versions of Windows, but does not work on 64-bit versions of Windows.