Consider GUI wrappers the "for dummies" version.
By the way it's always easier to teach a not particularly bright person to use a textual dialogue command line interface than a complex GUI: you just tell them (and let them write down) what do they have to type, what response they can expect and how are they to respond to it if it's this or that. I can remember how easy it was to teach my granny to use the UUPC e-mail system under DOS and how much harder it was to teach GUIs.
And strictly speaking, it is built on top of Libav, although they are considering switching over after 1.2
Consider WebM4Retards[0]. It provides a simple UI for some avisynth filters + ffmpeg while also allowing you to export the avs scripts and ffmpeg command line if you want to run them manually. It fills a particular niche between simple transcoding/muxing and non-linear video editors plus encoding pipelines.
Additionally GUIs can help with tasks that you execute infrequently enough that you don't manage to memorize the myriad of command line options. MeGUI is convenient when adding chapter information to a video which I do once in a blue moon. In principle I could do this with text files and mkvtools, but it's just faster to use the GUI than reading the manual (again).