When I download a .rar file or a .7z file and double click it, I am told that the "Archive Type is not supported." there should be a download button under that that allows me to quickly and easily download the required programs, such as rar / unrar. If the program is proprietary, the EULA should pop up. Doing this would make it easier for newbies to use Ubuntu, and save time for me.

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After reading comments, it would also make sense to do this with most file formats, though I think it might already do this with certain media formats. Ex: Does it do this with .mp3s?

Other compression programs such as 7zip provide detailed information on activity progress, such as time elapsed, estimated time remaining, current compression ratio, size compressed, compressed size etc. Feedback from archive manager is poor and progress cannot be judged.