Brian wonders whether project Stimpy became Outlook Express.
As noted in the article, projects Ren and Stimpy were merged into a single project, which became Outlook. You could say that Stimpy became Outlook, too.
Outlook Express (code name Athena) was originally known as Internet Mail and News. This was back in the day when the cool, hip thing for Web browsers to do was to incorporate as many Internet client features as possible. In the case of Internet Mail and News, this was POP (mail) and NNTP (news).
After Outlook became a breakout hit, the Internet Mail and News project was renamed to Outlook Express in an attempt to ride Outlook's coattails. It was a blatant grab at Outlook's brand awareness. (See also: SharePoint Workspaces was renamed OneDrive for Business; Lync was renamed Skype for Business.)
The decision to give two unrelated projects the same marketing name created all sorts of false expectations, because it implied that Outlook Express was a "light" version of Outlook. People expected that Outlook Express could be upgraded to Outlook, or that Outlook Express and Outlook data files were compatible with each other.
Code name reuse is common at Microsoft, and for a time, the code names Ren and Stimpy were popular, especially for projects that were closely-related. (As I vaguely recall, there was a networking client/server project that called the server Ren and the client Stimpy. But I may be misremembering, and Ren and Stimpy may just have been the names of the two source code servers.) You may have heard the names Ren and/or Stimpy in reference to some other projects. Doesn't mean that your projects are related to any others with the same name.