Apache-2.0
This is not legal advice. Read disclaimer.
Atlantis was originally copyrighted and licensed under: Copyright 2017 HootSuite Media Inc. 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. In 2018 it was forked from github.com/hootsuite/atlantis to github.com/runatlantis/atlantis. The contents of files created before the fork are obviously still under the Hootsuite copyright and contain a header to that effect in addition to a disclaimer that they have subsequently been modified by contributors to github.com/runatlantis/atlantis. Modifications and new files hereafter are still under the Apache 2.0 license, but are not under copyright of Hootsuite Media Inc.
Source: github.com/mbeacom/atlantis@v0.4.3/LICENSE