Download managers are mostly snake oil (i.e. fake cures for an imaginary problem).
Modern browsers can pause and resume downloads, or can get a plugin.
Their main use today is in multiple downloads, or automated downloads, or limiting connection speeds e.g. to prevent a content distributor being overloaded.
This does not answer the question, it only states your opinion and gives a lacking definition of what a download manager is.
To answer the primary question, I will list commonly used download managers in OSX:
App Based:
JDownloader (Open-Source)
Folx (Similar to DownThemAll! in Firefox)
Speed Download/ Speed Download Lite
There are others but I find these are the most commonly used. I've heard JDownloader is good, but I was never able to get it to work well. Folx worked great for me, and it will handle multiple slices/downloads at a time. Not free however, worth it I find.
[Edit]I've now been using JDownloader for some time now, I'm happiest with it of all the other downloaders. it isn't automatic, but if you secondary click/right-click or Cmd-C Copy the download link, JDownloader grabs right away and checks if download link is available/online. It's nowhere near as good as IDM, curl, or DTA! for Firefox, but it's up there.[/Edit]
Never been a fan of Speed Download.
If anyone else has other options or insights, would love to hear them. I'm always open to trying new apps.
