I am working on porting an existing business application to a new platform, which combines some of the aspects of work on an existing app, and some new stuff.
Its new because everything is going from Windows Forms to ASP.NET AJAX, and there are several changes involved in that process when it comes to the GUI and event based side of things, but its also partially work with existing stuff because the business rules are the same, the database is the same, although we have been gradually making improvements as needed to those.
On the other hand the company I work for supplies grocery stores which have been affected positively by more people eating at home, so despite being in Michigan, things are going well for the company, and we can afford to move this app onto the intranet.
The nice part about doing this is I get to learn all the new platform stuff, but we don't have to go out and get user input for some new set of use cases, plus we can work with the input we've received from the WinForms version.