Software installation, packages, and dependencies
The definition of a software package is quite broad. In the early days of computing, when computers were exclusively used to solve mathematical problems, most programs were written completely from scratch to run on a specific computer, so there was no need for installation and thus no need for the concept of software packaging. For a long time afterward, software was still synonymous with executable files. Installing a software product that consists of a single executable file is trivial —just copy it to the target computer.
Such software certainly exists today. For example, the maintainers of jq (a popular tool for extracting data from JSON files) provide standalone, statically linked executables that combine the program and all libraries it needs into a monolithic file and can run on any Linux system, so any user can just download it from its website (https://stedolan.github.io/jq/download/) and start using it.