Firebird adds new features with version 2.1

I suspect you don't know what you're talking about.

Using processes instead of threads doesn't necessarily make you 'heavy on 
resources'. It doesn't necessarily indicate that you are 'stuck' in any 
way at all. It requires greater discipline than using threads, and the 
context switch time is slightly higher, making it an inappropriate 
technique for insane loads, but in every other way using processes is 
*preferable*.

Think: what happens if a single MySQL server thread crashes. Who knows 
what state it corrupted first: best take the whole server down.

If a PostgreSQL server crashes, the others are unaffected, their address 
spaces inviolate save for a strictly-defined shared memory region: they 
can generally carry on.