The brainrot esolang is free to download and use on GitHub! Each update is posted there first, so there's no better place to go for a download.

An accessible web interpreter is also available, but more bugs may be present and it runs on an older version of the language than the fully up-to-date GitHub download.

There is documentation ready to read that outlines each and every data-type, command, syntax detail, etc, all at your fingertips.