I only use free Web hosting because I don't have the means to use a PayPal account or something similar. These two Web hosting providers allow script hosting, as long as you don't exceed their bandwidth or steal their server load:
000WebHost
XtreemHost, the one I'm using right now
XtreemHost also comes with your own ".co.cc" domain so you don't have to register on www.co.cc to get one. You can't use subdomains for each of your forums though, because you can only have up to six subdomains.
Note: Neither are 100% reliable. Also, in case you wanted to know, XtreemHost is a partner of Byet or whatever.