I've implemented a simple anti-bot scheme today, that requires comments and mails sent to me via this site to enter a fudged code.
The implementation is based upon the article: An ASP.NET Framework for Human Interactive Proofs written by Stephen Toub.
To check it out, simply click on either the Contact or the Feedback links on various portions of this site.
In 2017, with the release of Delphi 10.2 Tokyo, Embarcadero introduced a specialized implementation of the Observer pattern into the System.Classes unit. While it has been in the wild for 9 years, it remains a "hidden" architecture for many, primarily because it serves as the invisible engine behind LiveBindings. Other than live bindings, you can also use the Observer pattern as a way to update component settings to the Windows registry, an .ini file, or persist it elsewhere.
System.Classes