Tex has extraordinary capacity to do most anything you wish ( as you can see from the range of options here: http://www.tug.org/interest.html), but the more abbreviated the solution, the less one gets. John Forkosh created mimetex and mathtex and you can find out more about them at john's site, forkosh.com. The same applies to MathTran, asciimath, and mathjax. They are all subsets designed to provide an economical solution to addressing math online.
IMHO, if you want and need all that Tex can do, do a full install of Tex Live and use CPAN via tl_mgr to pull whatever packages or macros you might need.
I continue to hope that with the work being done on STACK and MathJax that at some point we will see, as was targeted by the MathTran project, full correspondence between Tex and Mathml allowing us to go in both directions, but that is a mammoth task and while lots of educators in the US opine about the issues we have with Math education, we see record profits for companies like Pearson while we see little investment in basic tools to make Math education possible.
In the meantime, one could hack on ASCIIMathML (see e.g., http://asciimathml.com/ ) and you can play with DragMath as well (via the xml files) as far as displaying directly via MathML
MathJax may well be the future of Tex on the web, but there is a long way to go