I am using Free download manager(FDM) as my permanent download manager from 1year onwards . The user interface is very interactive plus simple .There is no problem regarding the key as compared to IDM . It gets integrated to almost all the known browers . As FDM is an OPEN SOURCE SOFTWARE that’s why it provides range of features at no extra cost.I do like it’s FDM community which provides vital information regarding download links.
If you are looking for an ideal download manager then FDM is an alternative to it.