MediaWiki skinning
MediaWiki can have almost any look you want, because its look is determined by a "skin" that consists mainly of CSS stylesheets.
For instance, on chekmate.org we found this trick:
#p-nav,#p-search,#p-tb,#footer { opacity:0.83; } /* make a few corners round, only supported by moz/firefox/other gecko browsers for now */ #p-cactions ul li, #p-cactions ul li a { -moz-border-radius-topleft: 0.4em; -moz-border-radius-topright: 0.4em; } #content { -moz-border-radius-topleft: 0.6em; -moz-border-radius-bottomleft: 0.6em; } div.pBody { -moz-border-radius-topright: 0.4em; -moz-border-radius-bottomright: 0.4em; }