Metar Viewer - Metar Reader app for Android

While Metar Viewer - Metar Reader is not on the same level as Metar-Taf when it comes to functionality and polish, the former does have a couple of useful features that make it worth having on your Android device.

Firstly, the app is released under the open-source license (source code) and it doesn't cost anything. Secondly, the app lists air traffic control radio frequencies, which can be useful if you want to tune in to airport communications (provided it's legal in the country you are in). And that's pretty much it. Still, the app doesn't take much storage space, and doesn't cost anything, so there is no harm in having it on your device as a fallback option.