What software do you love?

Today marks the start of February, the "month of love." In commemoration, I want to ask you a question:

What software do you love, and why?

Some members of the high-tech illuminati start and end their discussions of design in terms of RAZR phones, iPods, and other cool gadgets. That's clearly where technology and coolness and the mainstream have all converged right now, and so I think it's only natural that people gravitate towards those topics.

But for my own curiosity more than anything else, I'm interested in shifting the conversation about desirability in design over into the computer software realm, at least for today. And I'm interested in hearing from you.

What's your favorite piece of software, modern or ancient? What makes it great? Is it something fun or something useful?

Can software provoke the same sense of "gotta have it" that a tech gadget can? What does it take to get you excited about software?

How much does a great user experience factor in to your feelings about a software product? Or is it all about the utility? Or about the people who make it? Or about attractive visuals? Speedy performance? Extensibility? Some combination of all of these factors?

What exemplifies a great software experience for you?

Use the Comments link below to tell me your thoughts.