Curl's "one thing" is to get files from the network in every conceivable way possible. Ffmpeg's is to convert media files between every conceivable set of formats possible.
Curl does loads of stuff, supports so many protocols - HTTP, LDAP, FTP etc.
CLI video editing
Make web requests
ImageMagick and gnuplot.
GraphicsMagick is like ImageMagick but much more sane & performant.