Files with .docx extension are Microsoft word files that usually contain rich text, images, tables and other objects. These files are used to create rich text documents. Most of the rich text editors can create and open docx files. Microsoft Word is widely used to create, open and edit Docx files.
Other text editing softwares like Apple's Pages, Open Office can be used to open docx files other than Microsoft Word.
Microsoft had a free Word Viewer that can be downloaded and installed to open docx files without Word or any other editor. The free Word Viewer is not longer available to download on official Microsoft site and they recommend installing the Word mobile app to view docx files on your phone. Other than than browser apps like drop box, google docs can also be used to view docx files without installing any software on your computer.
To view docx files on Google docs, simply upload the docx file on google docs and you will be able to open, view and edit docx file in your web browser. Google Docx is free to use and is a good way to create or open docx files.