Acrobot - Acronym Generator:

Lets you quickly convert blocks of text that feature well-known abbreviations and acronyms into something more accessible. This tool will wrap a <abbr> or <acronym> tag around any matched entries, thus, if you enter W3C, it will be converted to <abbr title="World Wide Web Consortium">W3C</abbr>.

(It doesn’t currently convert ABBR to &lt;abbr title=&quot;Abbreviation&quot;&gt;<abbr title="Abbreviation">ABBR</abbr>&lt;/abbr&gt;!)