Set your PC Clock from an accurate atomic clock on the web.  You can put
in on your website so that others can use it to correct their clocks
without having to install software or without you having to install
software on your server.
It only works on Windows and with 32-bit Java.  If I had access to a
64-bit C compiler I could make it work on Windows with 64-bit Java too,
but I do not.
Full Java source code included, and native C JNI code.
If you run the code as a standalone application, make sure you extract the
pcclock.dll and put it somewhere on your path, the path, not the
classpath.
Why the clock icon?  It should be too obvious to explain.