Finance is a Perl module which interfaces with the now defunct Mt. Gox API. It supports both the legacy API and the "key-secret" API (v0).
This open-source tool is useful to merchants as it helps determine "market clearing rate". This technique is needed because the number of units offered at the "best bid" or "best ask" are inadequate for a trade of size to execute. Thus the market clearing rate determines the weighted price for the entire trade to execute.