MHequ simplifies creating multi-column equation environments, and tagging the equations therein. It supports sub-numbers of blocks of equations (like (1.2a), (1.2b), etc) and references to each equation individually (1.2a) or to the whole block (1.2). The labels can be shown in draft mode.

Comments in the package itself describe usage.

The author is Martin Hairer. The package is Copyright © 2000,2005 Martin Hairer.