Omformaren is a free measure coversion software. It supports 401 different categories in 14 categories. It is very easy to use, and has a nice interface.

You can choose if you want the results from your conversions to be in standard of scientific form, and how many decimals you want. Omformaren also supports multiple languages, and if it is not available in your language, you can easily translate it yourself.

Omformaren is freeware, so you can freely use and distribute it, as long as it isn't changed in any way, and the copyright information is intact.