android-decompiler
Pretty much everything that is needed to extract things from apks +
example program which is used to extract proto definitions from apk files (see proto-gen).
I wrote most of this code two years ago in two days, then sorta updated it half a year ago, so do expect some bugs and create an issue if you find one or fix it yourself.
Installation
go get github.com/j4ckson4800/android-decompiler