If you expect to receive external contributions, the Apache 2.0 license can be a pretty good choice, because it has a clause to automatically grant you a licens

If you expect to receive external contributions, the Apache 2.0 license can be a pretty good choice, because it has a clause to automatically grant you a license on contributions (be them code or just ideas): > Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of this License, without any additional terms or conditions. I am using it for https://letsblock.it https://letsblock.it, so that I can ensure the filter corpus is in the right license without requiring a CLA.