

Free
Google Documents
All systems via web browser.
Google documents is a (mostly) online cloud based advanced word processor that is part of a web based office suite offered by google as part of google drives. You will need to setup a free google drive to use this service.
Review
Google office suite some major benefits over it's paid competitor Microsoft Office. The first being that it is free. Being web based it is 100% cross platform compatible. Some functions are a bit rough around the edges as related to MS Office but still functional. It is also very easy to share files with other people and even allowing people you decide to be able to edit. For light writing projects it is useful but those more complicated may prove troublesome.
Specification
Windows: Windows 7 and up, not including Windows Server editions
Mac: Sierra (10.12) and up
Google Drive, Docs, Sheets, Slides, and Forms work with the 2 most recent versions of the following browsers (unless specified otherwise): Chrome, Firefox, Internet Explorer 11, Microsoft Edge, and Safari.