Just to join in with the 3 villa boys, I snapped my ACL 18 months ago. Also tore my meniscus and slight knee fracture at the same time.
Sadly not being a professional footballer or in my 20s or 30s they deemed that an operation to fix my ACL (which basically involves creating a new ACL from tissue elsewhere on the body) was not necessary and could make matters worse. The ACL is basically a kind of rubber band inside the knee joint, so once it's snapped, it's gone.
So I just had to do loads of rehab to strengthen all the muscles in and around the knee and leg. I can still do most things but high impact sports are a no-no. But I'm 50 now so that isn't really something I'd be doing anyway.