Question: I know that the default answer is "it depends", but I want to know the feature list you are working from in developing a good application.

I'm particularly interested in features that need to be cared about at design time because adding them late will cost us a lot.

**Please list one feature per answer so we can vote for the most important features.**

Any extra info, like your own war stories, will be appreciated.

I ask this question to enhance my application from day zero, and I think I'm not the only one with this target, so please write whatever feature YOU think should be exist in a good application.

Answer: 
**Automation** - if application does not require UI for operation, then enable ability to execute using command line or script. Found many good FTP tools (archive tools too) that fundamentally do not need a UI to do the intended job, but are not script-able or do not have command line capability.
**Inbox**

although it seems to be a very small to mention, but it really has big effect on the usability of the application and the performance too
Imagine if user can ask a heavy report that may take some minutes to generate,   
instead of 'click and wait' he can choose 'send me the latest report when it is ready'