JDownloader

addon that adds rightclick option (optional) and you can set minimum downloadspeed in settings or per file and it will restart file if it drops below speed that user set.

this addon should check for resumable flag (only restart if user say to restart non resumable downloads)

maybe adding a reconnect feature too, but this can also be done via eventmanager once it is finished

also some % number needed when not to restart because there is no sense in restarting a file thats 98% complete ;9