First, interoperability matters. In my column last week, I spoke about how Microsoft is making some important steps towards opening up its networking protocols and increasing their interoperability. The days of having homogeneous clients are long gone: even the different versions of Windows have their interoperability problems. The reason that fax is so widespread is because just about anyone can send a fax to anyone else’s machine, with the prospects (mostly) of the document going through. The more our networks are interoperable, the more useful they can be for a wider group of knowledge workers.

The Web has made interoperability both more of a challenge and more of an opportunity, too. Look at how many different browser versions you are running across your enterprise, and within these versions, variations on Acrobat, Java, Flash, and other helper applications that are critical to how pages are displayed inside the browser.

Second, simplicity matters. The second reason that faxes mostly work is because they are dirt simple. You stick a page in the machine (the hard part is figuring out which side is being scanned), key in the ten-digit phone number, and press send. There are no command-key combinations, like Control-V-N, no software to load, and no upgrades to worry about (other than making sure you have paper and toner in the machine if you want to receive faxes). Some machines don’t even have on/off switches, making them even simpler.

Simplicity is an important goal when designing your next batch of applications, especially those that are going to take advantage of rich Internet interfaces like AJAX and Javascript. You don’t want to have to hire more programmers to build your applications, do you?

Third, real time communication matters. Witness how our own communications have migrated from phone calls to email, from email to Instant Messages, and from IM to texting. As our IT operations become more distributed, we need better ways to stay in immediate touch. Why fax works is because within seconds you can send a whole bunch of pages across the globe, and know that they have been received and can be processed by the recipient. That is one reason why email is being replaced by IM and texting – there is no guaranteed delivery on most email messages.

Finally, privacy matters too, but only with the right layer of authentication. Sending a fax to a computer, or to an eFax or other Internet-based fax account, is an easy and simple way to get a private message to someone. Sending an email to someone across the Internet is not private, and in some cases if you cc to everyone by mistake very public!

So the next time you have to build a new application, consider the lowly fax machine and what it does right. Take these lessons to heart, and you will have a leg up on building better and more useful applications.