Windows/Mac/Linux: LibreOffice, the open source, free alternative to Microsoft Office, just got a big update that adds in a ton of new features alongside a new cloud version you can install on your own server.
Among the highlights in the update are an improved text layout engine, table styling in Writer, improved spreadsheet compatibility in Calc, and keyboard shortcuts are now show in context menus to help you learn them. There are a ton of new features, and you can take a look at most of them on LibreOffice's landing page for this version.
There's also a new experimental toolbar that acts basically the same as Office's ribbon. You can enable that by first enabling the experimental features under Tools > Options > LibreOffice > Advanced > Experimental features. Then head to View > Toolbar Layout > Notebookbar.
Also new is the first full source release of LibreOffice Online, which adds in collaborative, in-browser editing of documents. Essentially, it's a private Google Docs that you host yourself. It's meant mainly for enterprise, but that doesn't mean you can't install it on your own server if you want, though you'll need some technical skills to do so. You can learn more about how LibreOffice Online works here.