Creating an extranet can be quite an expensive and time-consuming task. However, to cut corners and over-runs on costs, you can use WordPress, assorted plugins, and web server security routines such as .htaccess and restricting IP access.

Elegant Themes/Divi crew

Elegant Themes has some interesting approaches as well as using Wiki-based plugins.

WOffice

Tried an install of WOffice on ThemeForest and the WOffice website, which is a WordPress theme, but is hacked up out of other plugins which would TECHNICALLY work, but the demo implementation is not 100% working and the “one-click access” is definitely not it.

They run a good game in the documents, but in practicality, it needs a lot more work. I may try this again from scratch because the demos and screenshots look spectacular, but yeah not build this yet. Also, the annual fee for GPL’d software is a bit over the top for the quality seen here.