OnlyOffice, is an open source office suite developed by Ascensio System SIA. OnlyOffice is most commonly deployed as a SaaS (software as a service), Similar to Google Cloud or Office 365 for Business.
The OnlyOffice desktop version has a document editor, a spreadsheet program and a presentation editor. All of the apps have look and function MS Office 2004. OnlyOffice can open all the MS Office formats. In fact the MS Office formats are the defaults.
Caution! Do not accidentally install the OnlyOffice server. It take loads of disk-space and time to install and it is not at all what you need.