Convex is a easy perl program that allows you to convert numbers from one currency to another. Its user interface is designed to be extremly fast to use for normal www etc use.
The source of the 0.3 version is available in http://www.acr.fi/convex/convex-0.3.tar.gz. Read the README for more information. This program is distributed BSD style license. Read the COPYING for more information about the license.