Internet Download Manager is not available for Mac but there are plenty of alternatives that runs on macOS with similar functionality. The best open source Mac alternative is Xtreme Download Manager. If that doesn't suit you, our users have ranked more than 100 alternatives to Internet Download Manager and many of them are open source and available for Mac so hopefully you can find a suitable replacement. Other interesting open source Mac alternatives to Internet Download Manager are AB Download Manager, aria2, Open Video Downloader (youtube-dl-gui) and Persepolis Download Manager.
I think that XDM is a very good alternative to IDM because it allows you to download videos on many sites other than YouTube (ENI platform, LinkedIn for example) like IDM does. On the other hand, IDM sometimes preserves the file name while XDM does not, which is annoying if you download a series of videos because you have to rename everything by hand. Translation FR OK.