What is Fortress?
Checkout the What is Fortress? page.
Is Fortress Dead?
No. Fortress is still alive and supported. As of late 2003, most developer effort is going into Merlin, but there are still plans for Fortress 1.1 and beyond. Some of this includes updating Fortress to use the new meta package, a default CLI and servlet environment, and more. If you have specific requests, send an email to the users list.
What happens to Fortress once Avalon5 is released?
Fortress is slated as Avalon 4 reference implementation & Merlin is slated as avalon 5 implementation. According to avalon5 proposal Define Fortress as the Avalon 4 reference implementation. Promote Merlin as the eventual Avalon 5 reference implementation.
Is fortress going to be deprecated once avalon5 comes into picture?
When should I use ECM instead?
Never. Fortress supports all of ECMs features, is better designed, more extensible, etc. The only reason to use ECM is because you are already using it and don't want to upgrade.
How do I extend the Fortress Configuration
See the page titled How do I extend the Fortress Configuration?