Third-party gadgets are gadgets Google didn't create, but are available in spreadsheets. If you're looking for help on how to use these gadgets or need to report a problem with one of them, the best place to do this is to post in the Google Docs help forum.
You can also do a Google search for the creator's contact information based on the info listed beneath the gadget.
Note: if a gadget's creator supplies us help information, we'll link to it from the help window
For more information on gadgets in Google Docs, visit this help article on how to get started with Spreadsheets Gadgets.
Interested in creating a Gadget of your own? Check out the Google Gadgets API and the Google Visualization API.
For help using these APIs, visit the Google Visualization API forum and the Google Gadgets API forum.