The W3C came up with a recommendation called MathML, which is a form of XML used to describe mathematical symbols online. Unfortunately, support for MathML is low and it is extremely verbose. 

For example, here is an equation $x=\frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$, that is rendered in \TeX\ like so:

\begin{verbatim}
     x=\frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
\end{verbatim}

and rendered in MathML like this (source \href{http://en.wikipedia.org/wiki/MathML}{wikipedia}):

\begin{print}
\begin{verbatim}
<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <eq></eq>
    <ci>x</ci>
    <apply>
      <frac></frac>
      <apply>
        <csymbol definitionURL="http://www.example.com/mathops/multiops.html#plusminus">
          <mo>±</mo>
        </csymbol>
        <apply>
          <minus></minus>
          <ci>b</ci>
        </apply>
        <apply>
          <power></power>
          <apply>
            <minus></minus>
            <apply>
              <power></power>
              <ci>b</ci>
              <cn>2</cn>
            </apply>
            <apply>
              <times></times>
              <cn>4</cn>
              <ci>a</ci>
              <ci>c</ci>
            </apply>
          </apply>
          <cn>0.5</cn>
        </apply>
      </apply>
      <apply>
        <times></times>
        <cn>2</cn>
        <ci>a</ci>
      </apply>
    </apply>
  </apply>
</math>
\end{verbatim}
\end{print}

\begin{interactive}
\begin{verbatim}
&lt;math xmlns=&quot;http://www.w3.org/1998/Math/MathML&quot;&gt;
  &lt;apply&gt;
    &lt;eq/&gt;
    &lt;ci&gt;x&lt;/ci&gt;
    &lt;apply&gt;
      &lt;frac/&gt;
      &lt;apply&gt;
        &lt;csymbol definitionURL=&quot;http://www.example.com/mathops/multiops.html#plusminus&quot;&gt;
          &lt;mo&gt;&amp;PlusMinus;&lt;/mo&gt;
        &lt;/csymbol&gt;
        &lt;apply&gt;
          &lt;minus/&gt;
          &lt;ci&gt;b&lt;/ci&gt;
        &lt;/apply&gt;
        &lt;apply&gt;
          &lt;power/&gt;
          &lt;apply&gt;
            &lt;minus/&gt;
            &lt;apply&gt;
              &lt;power/&gt;
              &lt;ci&gt;b&lt;/ci&gt;
              &lt;cn&gt;2&lt;/cn&gt;
            &lt;/apply&gt;
            &lt;apply&gt;
              &lt;times/&gt;
              &lt;cn&gt;4&lt;/cn&gt;
              &lt;ci&gt;a&lt;/ci&gt;
              &lt;ci&gt;c&lt;/ci&gt;
            &lt;/apply&gt;
          &lt;/apply&gt;
          &lt;cn&gt;0.5&lt;/cn&gt;
        &lt;/apply&gt;
      &lt;/apply&gt;
      &lt;apply&gt;
        &lt;times/&gt;
        &lt;cn&gt;2&lt;/cn&gt;
        &lt;ci&gt;a&lt;/ci&gt;
      &lt;/apply&gt;
    &lt;/apply&gt;
  &lt;/apply&gt;
&lt;/math&gt;
\end{verbatim}
\end{interactive}

Pretty obvious why it didn't really catch on. However, probably a bigger problem with MathML is that it cannot be used to create diagrams \cite[686]{diagrams}.
