Unit Converter is a freeware tool that can take care of all your unit conversions even when offline. It has an easy-to-use interface and contains most of the units commonly encountered while solving engineering problems. With more than 900 units, you are likely to find the units you are looking for. Other features include the ability to quickly search for units and categories, and add user-defined conversions. Everything is built into a single executable file so no uninstaller is necessary. Its small file size makes it easy to distribute among friends and co-workers.
Version 5.4 adds ability to perform coordinate transformations from latitude/longitude to UTM (and vice-versa).