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.
- comment-pln: Comment macros for use in Plain TeX
- texfot: Filter clutter from the output of a TeX run
- figplace: Floating figures in Plain TeX
- plain-cm: Variable sized fonts in Plain TeX