Ask HN: Simplest tool to build a web app

How long is a piece of string?

Seriously though I would say PHP plus MySQL and Memcache for scaling. With a reasonably modern framework like Kohana PHP you can build stuff pretty quickly on dirt cheap, no brainer hardware. :)

As to XSS/DOS etc. that is down to your code and to the server setup - somewhat difficult.

Kohana, Codeigniter...how good is libraries/plugin support on these.. Any other competitors?

pretty solid. You get plenty of the basics (ORM, session handling etc) with the core package and there are a whole load of community built libraries (projects.kohanaphp.com)

I couldn't comment on CI too much: I stopped using it around 18 months ago.

I've been using Codeigniter - a PHP framework. It's very very well documented -- you have to read the documentation to see how good it is. And the input class is very good at handling most XSS/SQL Injection type attacks.

You can try Kohana.