Overview: SharePoint does not stack up against any single COTS product easily due to the size and functionality offered. This post is my opinion and I am not an expert in any of the competing products.
This post aims to list competitor products in a vary broad sense and tries to highlight the areas that where the product and SharePoint perform a similar function.
- Atlassian Confluence
- Lotus Notes
- Igloo - http://www.igloosoftware.com/
- EMC’s Center Stage
- Google docs
OpenText, lines up some of SP's functionality such as blogs, Wikis and document collaboration.