I find the forum to be "light" on resources and i'm happy with that :) Bootstrap is heavy - i use it on my main site - with dependencies on javascript. Light alternatives to bootstrap could be http://mincss.com/docs.html , https://milligram.github.io, http://furtive.co/ . Take a look at this http://sixrevisions.com/css/small-css-frameworks/ for a list of alternatives.