Are there any open source scripting engines that allow you to give your users the ability to perform light scripting on pages via a web based interface?
(some objects/collections would be pre-populated, and have security in place so users can't hack into the web application's inner workings etc.)
Examples:
http://wiki.shopify.com/UsingLiquid
Also I think vBulletin has some custom scripting engine and tags where you can do things like:
<if: user.isloggedin>
</if>
We had a lot of success with IronPython as our scripting engine.
We created a graphical UI that allows a user to modify a web page. In the background it generates a Python code and dynamically executing the code.
Java has the scripting framework (in Java 6) which would permit you (via the web) to submit a script in numerous different languages (off the top of my head, plugins are available for Ruby/Python/Javascript). The scripting engine can then run this.
Pages could be modified using standard JSPs, or perhaps via Apache Velocity or Freemarker templates.
I'm not sure how you'd implement a meaningful form of security, though. Perhaps via spawning off a new JVM with particular access policies. That may be a little heavyweight for some scenarios, though.