Sonnet includes Media Grid Overlay Manager add-on by LCweb. You can use Media Grid Overlay Manager add-on inside Sonnet for free. Please note that it is not a freeware though. You can not use it apart from Sonnet unless you purchase the appropriate license.
This documentation on using Media Grid Overlay Manager add-on is the very basic information you need to get started. Please take a look at the important links below that have additional information about using Media Grid Overlay Manager add-on.