This package is a virtual font setup for using old style digits by default with the OT1 encoded Computer Modern Roman upright fonts. The eco package does the same job for the T1 encoded EC fonts and is generally much better because the EC fonts are like that; but then again, OT1 encoded cmr is available for free in TrueType and PS Type 1 formats and has its uses in pdf files as a result.

The author is Rowland McDonnell.