The unofficial number of apps for Windows 8 from the tracking website, MetroStore Scanner, shows 38,704 Windows 8 apps available.
MetroStore keeps a count of Metro-style apps for Windows 8 and Windows RT and nine days ago, there were 991 apps hitting the store every week.
In the past nine days since we last reported on the number of apps in the store (37,892 apps), the number of apps has jumped by 812 or a rate of 631 new apps per week – slowing down from the last measured rate of 991  per week.
A look at the contents of Microsoft’s App Store tells us that the education section has the most apps, with 6,026 apps, followed by entertainment with 5,818 apps, and then books & reference with 4,913. There are 4,091 games apps, 3,652 tools apps and 2,731 news and weather apps. On the ARM platform, 39,040 Metro apps exist, 40,548 run on x64 platforms and 40,466 run on 32-bit x86.
Microsoft Working Hard To Bring In More App Developers, Announces New App Contests
Again we note that the x64 and x86 totals are greater than the total number of apps in the store, but this may simply not be reflecting pulled apps.
As we indicated in the last report, apps are of varying quality in the Windows Store and users are still waiting for Google and Facebook apps.
Still, the pace of apps today is much higher than the 400 or so per week that was the case a couple months ago. Â Microsoft is making special efforts to seed new apps through its efforts with Nokia and more home grown efforts as well. Â Over time, these will yield fruit.
[source]
