This is the legacy 1.x version of the PlayN library which is no longer actively developed. Active development is happening on PlayN 2.x which is hosted at playn/playn.
Unless you mean to be using the legacy 1.x version of PlayN (and potentially submitting bug fix or other maintenance patches), you should immediately proceed to the 2.x site.
Unless otherwise stated, all source files are licensed under the Apache License, Version 2.0:
Copyright 2011-2014 The PlayN Authors Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.