LSGIA: Help needed ASAP. Word processor where an Android can work on a document and track changes offline. This for collaborative document site and Mission creation. All I've found so far is Microsoft Office 365 which cost $100 a year. Do you know of anything free or less expensive?

Help needed ASAP. Word processor where an Android can work on a document and track changes offline. This for collaborative document site and Mission creation. All I've found so far is Microsoft Office 365 which cost $100 a year. Do you know of anything free or less expensive?