If you’ve ever written an Android application, then you’ve likely used a third-party library in the process. The library may even have been open-source, so that the community can view, copy and modify the code. However, the creators always retain certain rights over their project, and the form in which the authors express these rights is called a software license.
Quite a few continuous integration tools exist, but as soon as you narrow it down to options that properly support Android, it becomes much easier to pick one. Travis and TeamCity are viable options if you care primarily about the codebase compiling and passing tests, but do not need options for storing artifacts, signing them and publishing them. At Big Nerd Ranch, we have adopted Jenkins as our Android continuous delivery environment because it has enough extensibility for plugins to fully implement the entire deployment pipeline properly.