Back in June 2012 announced the 100,000-app milestone and by October the number hit 120,000. However, growth is slowing down. It took Microsoft roughly six months to go from 50,000 to 100,000 apps, but now it managed just 45,000 in 11 months.
Although it might look bad compared to bigger platforms, it’s worth noting that the vast majority of high quality app that are the mainstay of iOS and Android are already available for Windows Phone gear. As for Windows RT, Redmond doesn't like to talk about it, but it is not going well.