CrackMes are small programs that can be used to learn how to crack, or break the copy protection, of software without using legitimate copyrighted applications. The most popular CrackMe.de site was taken offline a few years ago with only mirrors of the original site. With this in mind, a new site has been created called Crackmes.one that hopes to fill this gap. Developer s4r hopes to continue adding new features such as expanded search functionality and the ability to rate individual CrackMe solutions.
Source: https://www.bleepingcomputer.com/news/security/new-site-resurrects-crackme-challenges-from-the-old-crackmesde/