An ActiveState runtime is a pre-built, installable bundle, that contains both a programming language and packages for developing in that language.
ActiveState uses the Platform to build featured runtimes like ActivePython and ActivePerl that contain a ton of useful packages for a great out-of-box experience across your entire development environment.
The ActiveState Platform allows you to customize unlimited runtimes of your own too, so you can tailor individual bundles to the specific requirements of any given application and scope each to their own environments.
One of the key reasons to build a custom runtime is that the ActiveState Platform is designed to provide for full reproducibility of past builds by storing all components of a runtime build, including:
Compiler and its settings/flags (note: users can’t currently change these)
Key packages
Dependencies and sub-dependencies
Transitive dependencies, which can change depending on the version of your language/OS
All of which are stored in a git-style version control system. While we’re not quite there yet, hopefully in the near future you’ll never find yourself in a “can’t recreate the build” situation ever again.