X-Plane 11 is available in Beta test format. This is a free (but very limited) version of the new flight simulator, which is a development of X-Plane 10 that is streets ahead of its predecessor.
The beta demo version is useful for testing the capacity of your computer to handle this program. It will run on a 3Mhz dual core processor with 1GB of graphics without too many issues. I bit faster processor (I have a 3.5Mhz quad core processor) and the sim runs smoothly. This sim is highly recommended - I shall have a full version in the new year when I have the cash to hand.
($60 for the on line download version - and you get the download version of X-plane 10 free on the same activation key.)