Converber

Converber's library of units has more than 300 entries in 22 categories including acceleration, electric current, flow, volume, and more. On the off chance that there is a conversion not accounted for, adding it is as simple as opening up the built-in conversion editor and adding it to the collection.

You can par down the list to a more manageable volume by setting up favorites for frequently used conversions or simply telling Converber to only show you commonly used conversions. Converber is freeware, portable, and Windows only.