QueryBuilder can be used on advanced search engine pages, administration backends, etc. to build complex queries or filters. It is highly customisable and can be used with many jQuery widgets like autocompleters and sliders.
It outputs a structured JSON of rules which can be easily parsed to create SQL/NoSQL/whatever queries.
I've recently started putting together a Tk-over-jQuery routine I'm calling web Tk (wtk). The idea is having full Tcl running on a server, with a Tk-like layer that sends commands to code running in a browser.