You wont get a freeware with an FMC anywhere, best bet is to download an IFDG or Project Airbus model off of Avsim, most these have a standard A320 panel in them then download a piece of software called VASfmc, then use that as the FMC for the Airbus, its pretty self explanatory when you get going, but for the VASfmc to work, click the button that says “AP Couple” this will then adjust your heading on your autopilot whenever you get to a waypoint in your route.

Hope this helps you a little
Josh