Well, DAP Free one is good if you can live with too many obtrusive Ads. Unfortunately I cant.

As Grr said, FDM is a good alternative, but you shouldn't expect it to be as good as IDM. Out of every alternative of IDM tested by me, FDM is the best choice.

For features like site grabbing, you can use better tools like WinHTTrack which does the job. Similarly for videos, you can use plugins available for free.