Nice useless meta tag. downloader is only a useful tag when people tell you just what downloader they are using. On its own it serves no purpose.
Only a few questions tagged with it so it's an easy kill.
I actually consider it semi-useful. There are quite a few programs and games out there that use either some custom downloader or something rebranded (generally referred to as downloader, at least in many communities I know) and they might be hard to identify based on the customization being applied.
However, how about making it a synonym of download-manager? While most download managers are more generic and allow you to download several things, downloaders are typically just specialized or limited download managers.