Until recently, Chromebooks could browse the Web and run dedicated ChromeOS and Android applications, and that was that. But things are changing now since Google announced Crostini, a technology to run arbitrary Linux applications on ChromeOS.
What you get, in short, is a Linux distribution running in a virtual machine. It is sandboxed, but with some channels set up between the virtual machine and the surrounding ChromeOS, so that e.g., icons of applications installed in the Linux VM show up in the ChromeOS launcher, and windows opened from within the VM are integrated with the overall ChromeOS desktop.
The default Linux distribution provided by Google is a Debian 9, and one should be able to also plug other flavours of Linux, at least in theory. But we can install applications as flatpaks there, at which point the exact Linux distribution becomes rather irrelevant, anyway.
How to set up your Chromebook to install flapaks is detailed elsewhere, so just follow those instructions. You can then browse flathub for the applications of your choice. But when you click on the “install” button for an app, things start to get a bit rough. The ChromeOS browser downloads a
….flatpakref file, but doesn’t know what to do with it, so stores it in the Downloads folder. The Linux VM can’t see it there (thanks to the sandboxing around that VM), so you first need to use the Files app to copy the
….flatpakref file from “Downloads” to “Linux files”. The latter is just the home directory of the Linux VM user, so when you switch to the Terminal app (which provides you with a shell for that Linux VM user), you can type
flatpak install ….flatpakref to finally install the application.
But there is also a more polished solution that doesn’t require falling back to the
flatpak command line: Just go back one more time to the Terminal shell to install GNOME Software in the Linux VM,
sudo apt install gnome-software gnome-software-plugin-flatpak. Then you can run the Software application from the ChromeOS launcher (it may hide in a “Linux apps” collection). Search for LibreOffice, install it, launch it, and enjoy.