Select and add modules before you actaully build and install operating system. Want to make a multimedia operating system chose your modules from the list. Just want to have graphic, editor and artwork tools, you can select those only. SLAX is very small, fast and eye candy Linux operating system with modular approach. It runs from the CD without installing the OS on the hard disk. You can even run it on a computer which is not having a hard disk or even on a computer wth crashed windows operating system. It can also work as a live CD which you can use on any computer and start working.
However SLAX Virtual Appliance also gives you an option that all the changes made to the filesystem can be saved to the virtual harddisk. This way even if your system reboots you have the changes saved. You can select modules according to your taste and build the ISO, so ISO size varies accordingly. Unbelievable, that slax has more than 1000 modules.