I’ve made a lot of wordpress plugins. A few plugins have come from using wordpress as an internal intranet / groupware tool. I’m one of the top wordpress plugin developers. My wordpress profile is found here and a list of the plugins below:
1) Facebook Comments – Import your comments from Facebook to WordPress
2) Allow Categories – Permission private / hidden categories by user
3) Private Files – Make sure users are logged in before they can view images / attachments (useful with allow categories)
4) YouTube Feed – Embed you tube videos in posts and detect Facebook feed reader, and convert to a link.
5) 3rd Party Authentication – Authenticate wordpress against gmail / google apps or email.
6) Post ToDo – Add a ToDo list to a post or page.
7) Limegreen – A plugin to read information from a limegreen update file.
8) WP Bible Gateway – Automatically insert links to bible gateway in your posts.
9) Force User Login Multisite – Force user login on a per role and per site basis
10) Database Read Replicas
11) Amazon S3 For WordPress with CloudFront
I also intend to eventually write a document mangement and SVN browser for wordpress. Oh, also I found this great site for plugin developers which documents the various “hooks” that you can use in plugins: http://wphooks.flatearth.org