Run full Linux distros or specific applications on top of Android
Another related app is Termux. It can't run full Linux distro but it is much more lightweight and it has a pretty active community at /r/termux.Termux wiki: https://wiki.termux.com/wiki/Main_Page
Termux repo: https://github.com/termux/termux-app
Subreddit: https://www.reddit.com/r/termux/