It's true that Windows Phone (and now Windows 10 Mobile) doesn't have as many apps as Android or iOS. However, the perception of that app deficit may be just as problematic -- why would you switch to a Lumia 950 if you assumed that none of your favorite apps had Windows equivalents? Microsoft clearly isn't happy with this state of affairs, as it just released AppComparison for Android to help set the record straight. The app (a spiritual sequel to the old Switch to Windows Phone) tries to match the Android apps on your phone with their mobile Windows counterparts, either giving you an exact parallel or the next best thing.
Whether or not you agree with the findings is another matter. It's good at finding some third-party software (such as Dropbox and Spotify), but it's evident that the company is reaching when it comes to apps from Google, Windows' best-known holdout. It tends to suggest apps and services that either aren't really analogous (UC Browser may be fine, but it's not Chrome) or would require a ton of reinvestment. Are you really going to transfer years' worth of Google Drive files to OneDrive? There are also some conspicuous gaps -- AppComparison didn't find a Windows match for Sonos' controller app, even though Phonos has been around for years. The tool should still be useful, but you'll want to double-check its findings before kicking your Android phone to the curb.