Once upon a time, there was a team developing two versions of a product, the first a short-term project to ship soon, and the other a more ambitious project to ship later. (Sound familiar?) They chose to assign the projects code names Ren and Stimpy, in honor of the lead characters from the eponymous cartoon series.
Over time, the two projects merged, and the code name that stuck was Ren.
When the project came up in a meeting with Bill Gates, it was mentioned verbally but never spelled out, and since Bill wasn't closely tuned into popular culture, he mapped the sound
The Ren team liked the fact that their name gave the boss the impression that the project was going to be a masterpiece of architectural beauty, so they never told him he got the name wrong.
Even though it has nothing to do with the story: The project in question is the one that eventually became known to the world as Outlook.