MAMP is a set of free softwares used to run dynamic web sites on servers running under Mac OS X. It stands for:
Once you installed it (as easy as usual) you can develop websites with php,perl,python and mysql functionalities.
Since I manage my website platform with Google Site, I use MAMP to actually create an intranet website for my collaborators.
When I plug my laptop to my lab's network, my local website is accessible to others through my IP at:
The ":8888" indicates the port you specified in the MAMP preferences panel for the Apache server (by default it is 8888).
Again, any collaborator connected to your intranet will be able to access your local webpage.
I think this is more powerful than the classic "Web Sharing" you'll find in "Sharing" panel of Leopard preferences because here you have mysql and php servers running.
The webpage you make accessible this way are localized in the /Applications/MAMP/htdocs/ folder (again by default).
I think this requires the webpage folder to be the default one to work.