Wouldn't that be cheating? Engine use is prohibited during a game.
Chess evaluation

not to be used during the game, but after. to see where you to or the opponent won/lost the game.
id like to run with lines that maybe i should have taken or practice with lines that maybe statistically werent as good in an attempt to improve.
Chess.com has computer analysis, which is good, and i use it alot, but it doesnt allow me to input random moves and see where the game would have took me, should i have played them.

Oops, my bad. Didn't understand what you meant by "on the fly. Lots of free or pretty cheap GUI/engines available. I prefer commercial stuff like Fritz, HIARCS, or ChessKing since it seems a little easier to use but lots of folks swear by the free stuff. Here's a search for "best free GUI", but you could also do a Search Forums for best free engine and come up with some leads. Or as I said, commercial stuff can be had for less than $50.
http://www.chess.com/forum/search?keyword=Best+free+GUI
I understand Chess.com has the ability to review games. and give values to who is winning the game. On my phone (android) however i can input moves and see instantly who is winning/losing the game and whether or not the move played was best...
Saying this, does Chess.com offer an on the fly chess evaluation software? ive been looking for a while now and i cant seem to find one!
any help guys?
thanks :)