By default, the search bar in Google Sites let's you search pages & documents on the site. But you can also create a custom search engine with Apps Script and add it to the Google Sites search bar. Here's an example where I let people search for files in a Drive folder:
"Many developers have come to prefer JSON for data serialization, but we recognize that good ol' XML is still an important format for many Apps Script users. Our existing XML service is good at parsing XML, but has limited ability to create or alter existing documents. In order to provide a more complete and consistent experience, we have created a new XML service, which launches today. The new service is accessed using XmlService, in contrast to the old service which was simply called Xml."
"During a recent Google Apps migration project, we received several requests to create custom groups of contacts so that users could more easily email frequent collaborators. Before switching to Google Apps, users created their own private distribution lists — but this approach led to overlapping groups that quickly fell out of sync.
The problem was a perfect case for Google Apps Script. We built a great solution that gives users as much power as possible with just a quick administrator review."
"We've shown you the wonders of Markdown as great for your to-do lists and notes. If you love Markdown too but you're stuck with a bunch of Google docs that aren't in the format (but need to be), this Google Apps Script converts them instantly."
The XML Service can be used to parse HTML. But it can be a bit cumbersome to navigate through the DOM tree. In the examples below we will see how to make that easier with things like getElementById(), getElementsByClassName(), getElementsByTagName().
"Access control to Google Analytics data is very coarse. Via the web interface you can have full access or none at all. Given the growing interest in data driven decision making at all levels of the institution I thought it would be beneficial to demonstrate how Google Spreadsheets and Google Apps Script could be used to selectively distribute Google Analytics data."
"In this special GDL, you'll learn how to use the new Drive API capability to import and export Apps Script code. This will allow developers to write tools to work in other development environments other than the Script Editor and also integrate with source controls."
" I frequently use Google Spreadsheets as a lightweight database, by setting up some columns, encouraging my colleagues to update it, and subscribing to notifications of changes. Then I export the spreadsheet as JSON and update a json file in our codebase. Sometimes I also just use the jsonp output of a published spreadsheet, but if I'm worried about performance or the information getting mis-updated, then I'll use the export-and-update approach. In order to export it as JSON, I used to use a Google Spreadsheets Gadget but now that those are deprecated, I use a Google Apps Script."