bellmac – Outline scheme for form letter production
The scheme is part of the author's AutoLetter package.
Maybe you are interested in the following packages as well.
- knuth-letter: Knuth's example letter macros
- letter-plain: Letter macros for Plain TeX
- lettermac: Simple macros for writing letters (Plain TeX)
- twocolumns: Knuth's two-column output macros