Can I use my phone as a bluetooth game controller for my computer? I've seen BT Controller but I think it only allows users to use their android as remote for other androids. I just want to use my phone as a bluetooth controller with up, down, left, right, L, R, start, select, A, B buttons for my computer. Is there an app that makes this a possibility?

Basically, there are generic bluetooth game controllers that can be bought on stores. I was wondering if I can make my Android phone act like such and be used on computers.
You haven't mentioned which types of games you need this for but there are several possible options:

Gmote 2.0, which is a client/server type system which would let you use your Android tablet to control your computer.

RemoteDroid, which is similar to Gmote, it also uses a client/server system.

GRemotePro may be the right choice for you as it is but you need to pay for the server software. It is specifically advertised as being for game control.