• It fits on a floppy. Ideally, it doesn’t exceed the psychological limit of 1MB.
• What it does can be described in one simple sentence.
• Its creator had a strong interest to make it. Or better yet, a personal need.
• It’s not trying to outsmart you.  (If you ever spent half an hour killing all the annoying auto-whatever features in Word, you know what I am talking about)
• It was made by one person, or at most by a small group of people.
• It’s free. It’s not always true, unfortunately.
• You can play with it. By playing I mean something very serious.
• It’s better or easier to use than good old pen and paper.  If you look deep into your heart, you have to admit that many programs fall short of this.

Here are some examples

• Tom’s eTextReader
• TreeSheets
• ProcrastiTracker (I was considering for a moment to switch back to Windows to be able to use it)
• Vim (Well, of course)