If you only need the core libraries (not the IDE), version 6.6.0 libraries are available via Maven:
<dependency>
<groupId>net.sf.jasperreports</groupId>
<artifactId>jasperreports</artifactId>
<version>6.6.0</version>
</dependency>
However, this article focuses on the Studio (the GUI designer).
If the official site doesn’t provide direct links, search with exact phrases: tibco jaspersoft studio 6.6 0 download
"jaspersoft-studio-6.6.0" download
"TIBCO Jaspersoft Studio 6.6.0 final" site:sourceforge.net
Avoid third-party “download managers” – stick to SourceForge or Jaspersoft’s own archive.
If you have a commercial license for Jaspersoft Server 6.6.0: If you only need the core libraries (not the IDE), version 6
Windows:
macOS:
Linux: