http://groovy-lang.org/releasenotes/

4.x
https://e.printstacktrace.blog/these-10-new-features-make-groovy-4-0-awesome/
    https://github.com/wololock/groovy-4-examples
    https://www.youtube.com/watch?v=fTxFa2Sb4ts
    https://habr.com/ru/company/otus/blog/702356/
3.x
https://groovy-lang.org/releasenotes/groovy-3.0.html
https://www.infoq.com/articles/groovy-3-new-features-java/
2.x
http://groovy-lang.org/releasenotes/groovy-2.5.html
https://www.infoq.com/news/2018/07/apache-releases-groovy-2.5