For a free, light, and viable alternative to the Microsoft Office suite, Kingsoft Office may be what you’re looking for.
Downloading and installation are quick, and the suite in comparison to Microsoft’s official product line is much lighter on system resources. This is due in part to the fact Kingsoft only bundles three programs, whereas Microsoft’s suite offers a handful more—for a steeper price.
Upon starting either Kingsoft Writer, Spreadsheet, or Presentations, the interface is clean and suspiciously reminiscent of the ribbon layout that comes standard with Microsoft Office. For those who aren’t fans of multiple tabs, you also have the option to have all buttons revealed on the top toolbars, similar to Word 98.
Kingsoft Office is capable of saving in all supported file extensions—such as .doc, .ppt, .xls, and its own file extensions—with no trouble. When it comes to opening formatted files and documents from Microsoft into Kingsoft, cross compatibility is also not much of an issue.
Personally I did not encounter too many setbacks while testing this program but did experience a frozen screen once in a while; as with any alternative program, your mileage may vary, so check it out for yourself and see.
The Kingsoft Office suite is available on Windows and Linux operating systems along with Android and iOS mobile devices. The free version is, of course, free, however if you’d like to upgrade to their professional suite, it will cost you $69.95. You can download both the free and paid suite from their web page, found here.
Alternatives: LibreOfice (open source)