My first experiences with HORDE were many years ago, and I remember it being a very basic email client at best. Since I switched to Squirrelmail, I never looked back. So it was a surprise to see that the "HORDE application framework" consisted of so many applications. It appears that HORDE is able to hang with other full-featured Linux clients, and potentially extend them via their massive list of HORDE drop in applications.
Support for standards like WebDAV, SyncML, and in a near future release, CalDAV, was a surprise for me, as was the newly Ajax-ified interface. Because HORDE has matured into a full framework, running apps based on the framework is easy, so installing everything from a guestbook to a wiki is not only quick and painless, but managed via a centralized framework.
If you are a network admin for a small company needing an inexpensive but extensible web solution, HORDE might be worth a second look.