iUnit is a shareware unit conversion program for the Macintosh. It also contains many physical constants. The registration fee is only $20.
Using iUnit is easy. Just select the type of conversion you'd like to perform from the Conversion menu. For example, if you'd like to convert between feet, inches, meters, and other units of distance, select Distance. Then select the unit you'd like to convert from, by clicking the button next to that unit. Then type the value in to the box above the units, on the left side. All of the converted values will appear on the right side of the window.
For example, below we've selected to convert distance. We've selected foot as our unit of measure, and entered in a value of 5.75. This means that we are converting 5.75 feet into other measurements of distance.
 
As you can see above, the values of each unit of distance are seen in the right hand column under the heading Conversions. In the row for inch, we see that 5.75 ft is 69 inches.
You also will see the abbreviation for each unit of measurement on the right hand side of the Conversion column.
iUnit can also convert between various major world currencies. These are broken up into two categories, the European Union currencies, and the rest of the world. The exchange rates between the EU currencies are fixed, while other currencies vary. Two text files contain these exchange rates, called euro.txt and currencies.txt respectively. You can manually update these files, or download a new currencies.txt file as often as necessary.
The URL to download a new file is ftp://ftp.engresource.com/pub/currencies.txt
Just replace the currencies.txt file with the new one, making sure it is in the same folder as the iUnit application.
Finding the values of physical constants is just as simple. Select the type of constant you're looking for from the Constants menu, and a listing appears.
