Windows keyloggers.

<h3>can operate in "stealth mode"</h3>

<ul>
<li><a href="http://code.google.com/p/freelogger/">freelogger</a>
    <ul>
    standalone .exe, no install, launches with a tray-icon, but you can hide the icon after startup
    </ul>
<li><a href="http://sourceforge.net/projects/pykeylogger/">pyKeylogger</a>, Python
<li><a href="http://www.rohos.com/kid-logger/">KidLogger</a>
    <ul>
    They want to upsell you, though the source code for the lesser version comes with a BSD/MIT license, so they can't annoy you that much.
    </ul>
</ul>


<h3>can never operate in "stealth mode"</h3>
<ul>
<li><A href="http://code.google.com/p/klog-sharp/">klog-sharp</a>, C#
</ul>