Speed Download is a download manager and file sharing tool for the Mac. There are two versions of this app: Speed Download and Speed Download Lite. They vary only in that the Lite version is a stripped down version of Speed Download, which only allows you to use the download manager. The rest of the features are not available in that version, but you are saving $5.
Speed Download allows you to download files just like you would from your web browser. In fact, when you install the app, it integrates with your web browsers, so any download that you start from your browser will be taken over by Speed Download. It will be accelerated, too, since the app uses a downloading engine that can boost up speeds considerably. Of course, don't expect this to double your download speeds or anything like that.
There are a few other features in the complete version of this app. For example, it has an FTP client and a tool to upload files to Rapidshare quite easily. It also can connect to your iDisk and browse it, and you can download files from it as well. There is also a "send" feature that allows you to send files to other Speed Download users, or to a variety of other server types.
In a nutshell, this app works very well, it integrates with Chrome and other web browsers and it has quite a few features. It also has a simple mode for those who prefer it.