Picking up one entry for each category was no easy task because applications are divided between GTK and Qt, and there are programs that run in the console and do their job perfectly and are more lightweight than a GUI application. As such, I decided to leave terminal applications out of this review in the first place, but I provided a link below to an article which covers those. Applications listed below are built using various toolkits, not just a single one like GTK, however they are among the most lightweight graphical tools from their category.

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CMus
This is one of the best, feature-rich players for console. Built using ncurses and thus offering a text user interface, CMus has several view modes, organizes your music by artist/album, provides playlists and a library view, a filebrowser, it allows searching, Last.fm/Libre.fm scrobbling via this script, and it uses Vi-like keyboard shortcuts. A complete review can be found here and a guide to using it here.
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CMus is a powerful, feature-rich music player for the terminal which uses the Ncurses library:

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