Last modified: 2014-03-09 11:54:23 UTC
Now that Math is a separate extension, this should be one of the possible output types in $wgDefaultUserOptions['math']
JSMath seems to be unmaintained, and MathJax is the successor. There's already a MathJax extension (http://www.mediawiki.org/wiki/Extension:MathJax), but that also seems to be unmaintained. (And it's functionality really should be folded into this extension anyway)
See also bug 31406 comment6.
MathJax is being actively pursued now; bug 31406 and friends are successor to this.