I know this thread is a tad old, but I came across it having the same question. So, I thought I would share my findings in case others stop by.
du: The du (i.e., disk usage) command for Linux OS reports the sizes of directory trees inclusive of all of their contents and the sizes of individual files. More info here.
dot: A program for Linux that renders dot files (plain text graph description language) that produce certain type of graphs. More info here and here.
aspell: An open source spell checker. Check it out here.