Downloadable tool to convert between over 2000 units in many categories.

Handles metric, imperial, US, and user-defined units for common and engineering measurements. Includes common constants. Customizable for Win9x and later versions. By Josh Madison.

Firefox extension for contextual unit conversions, timezone conversions and currency conversions.

A unit conversion utility for students, teachers, and practitioners in engineering. Offers a wide range of categories.

Free conversion of multiple units of measurement. Used by scientists, mathematicians, engineers, students and business people.

Free software by Dmitry A. Kazakov. Includes details of the features, ready-to-use executables and user guide.