We’ve noted several times that we employ the Windows Phone app store (known as the ‘Marketplace’) as a baramoter to measure the health of the smartphone line. If development activity and app downloads and sales are up, then it’s a good indicator that things are at least not stagnating. We’re forced to use such secondary metrics as Microsoft is quite mum on the issue of how many WP7 handsets it has sold.

Today we have a new number that may say quite a lot about what’s possible for developers on the Windows Phone platform: an indie game has hit the 100,000 download mark. Now, other apps have done the same, undoubetedly, but having the official Facebook app hit the mark isn’t quite the same as having a game built by unknowns is.

The app, Taptitude, is a game that is a collection of puzzle challenges that the development team, FourBros Studio, updates weekly. Some 54 mini games are included in the application. According to the team, the app, which is free, has nearly hit $100,000 in total revenue. Not a bad check for an indie game on a yet unproven platform.

We’re going to be careful with our next words, but I would say that this bit of news should be taken as encouraging by fans of Windows Phone. This sort of story is exactly what brings in fresh development talent and blood to a mobile platform. Sure, there are now 50,000 Windows Phone apps, but that is hardly enough. Out of 50,000, only so many are worth your time; the current app economy is more chaff than wheat.

Kudos to FourBros, but we want to see who will be next to hit the six figure range.