I've been experimenting some with XMLRPC in Second Life.  This allows me to create a web page and send a message directly into the Second Life world.  It does not have to be a web pages sending information.  I could also use any sort of computer program.  

I've used this ability to create something I call "Encog's Particle Machine".  Encog's Particle machine is a web page that allows you to specify paramaters to create a particle effect in Second Life.  Particles are used to create all sorts of effects in the Second Life world.  The web page will communicate the particle information to an object inside of Second Life so that you can see the particles.  You will not be able to see this unless you are logged into Second Life.  You can see an example here.

[img_assist|nid=245|title=Encog's Particle Machine|desc=|link=popup|align=left|width=100|height=75]

You can access Encog's Particle Machine at the following address:

http://www.heatonresearch.com/examples/particle/particle.html