Yes, Flathub, aka the de facto app store for Flatpak, the cross-distro containerised app distribution method.
OnlyOffice Desktop Editors — note: the suite is technically styled “ONLYOFFICE Desktop Editors” but I refuse to shout 😆 — is a free, open source set of office apps inspired (partly) by the look, feel and feature set of Microsoft Office.
The suite “…combines text, spreadsheet and presentation editors allowing to create, view and edit documents […] without an Internet connection. It is fully compatible with Office Open XML formats: .docx, .xlsx, .pptx,” according to the Flathub app store listing page.
It’s not a Flathub exclusive though; users can still download OnlyOffice Linux builds from OnlyOffice website in a variety of formats, and the suite is available as on the Snapcraft.io Snap store too.
There are also official builds for macOS and Windows platforms, plus an ‘enterprise’ option and support for integrating with cloud storage platforms like NextCloud.
But in adding itself to the shelves of the Flathub store, OnlyOffice can now reach more users, particularly on Linux distributions that support Flathub out of the box, like Linux Mint 19 does.
If you’re keen to try it out for yourself you can learn more on the Flathub store: