The only requirement to access Stratus is a web browser, but certain features may have additional requirements.
Limited coauthoring is possible using the online Word “Web App,” but for the best experience, a full desktop version of Microsoft Word is recommended. Coauthoring requires Word 2010+ (PC) or Word 2011+ (Mac). Office 365 plans with a desktop component will work fine.
Offline sync for files stored on Stratus requires the “OneDrive for Business” sync client – not the “Next Gen” sync client. At the moment, this is only available for Windows, but Microsoft will be releasing a Mac version soon, and eventually will support Sharepoint sync in the “Next Gen” client as well. Note that this is distinct from the consumer “OneDrive” client.