You're not going to find anything that uses all 4 axes together without spending a lot of money.
MeshCAM will do indexed 4 axis, where the X and Y are doing the cutting, but not the A? I would think the DeskProto method would be better, as you are not recutting areas as you would be with indexing.
If you register Fusion 360 for a hobby license, it's free. But it doesn't support continuous 4th axis either.