Webinator may be obtained from
http://www.thunderstone.com/webinator/
.
There you may review the different versions that provide varying size limits
and levels of support. Then, you may download the free version or order
one of the paid versions.
Follow the instructions on the web site to acquire the package for your operating system. After registering for the free version, you will be given a URL to a compressed tar file for Unix versions or to a setup exe program for the Windows version, and this will contain binaries for your specified operating system.