You dramatically shortchange Doug Engelbart when you state that his
primary contribution was the invention of the mouse. That's the
smallest tip of the iceberg. Engelbart's lab can be credited with
pioneering work in video conferencing, shared screen computing,
screen-based text editing, document sharing, multiple windows,
email, online publishing, trackback links, hypertext, spreadsheets,
version control and graphics. But these were just means to the end he
envisioned of augmenting the cognitive capacity of teams of humans
by using technology.

For a terrific graphical overview of Engelbart's accomplishments, see:
http://www.visualinsight.net/_engelbart/Engelbart_Mural.jpg