maybeload – Prevent reloading of files
Defines a command \thisfileis, which will become \endinput if it's called for a second or subsequent time with a particular file name.
Maybe you are interested in the following packages as well.
- rcs-pln: RCS data in Plain TeX documents
- perfectcut: Nested delimiters that consistently grow regardless of the contents
- lettermac: Simple macros for writing letters (Plain TeX)
- twoside: Two-side typesetting in Plain TeX