So Litespeed works like apache and mod_php?
Yes.
No other server is needed?
No.
No load-balancing?
It load balances automatically in term of creating and destroying server processes on the same box, just like apache+mod_php. (If you want to distribute your load over several boxes you have to use the standard means of doing so, just like with any solution.)
I can run several application in one domain?
Yes.
But I have to pay for it if it runs on a server with more than a single CPU?
No. This is a common misconception. You can run Litespeed on multiprocessor boxes, but it will only utilize one processor in that case. The free version supports up to 150 simultaneous requests, which is extremely high. You won't hit that ceiling in a long, long time. You can regard the free version as more or less unlimited.
Sorry for the questions, I'm a newbie to RoR and I try to understand how it acts compared to php I'm currently using.
You will find that Litespeed operates more or less exactly like apache and mod_php. It is completely beyond me why people persist in using mongrel clusters nowadays. Litespeed is so much faster and easier to use.
/ Peter