If the online bookstore offers online payment, customers of the bookstore won't be happy if you deliver the software without security in place, or with an ever changing user interface.
Licensees are free to create derivative works of open source software and are free to distribute those works without payment of royalties to a licensor.
被许可方可以自由地创建开放源码软件的派生作品，并可以自由发布这些作品，无需向许可方支付版税。
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The software simplifies the whole administrative process of invitation, registration, participant management, payment handling and ticketing.