diff in octave and octave-forge

[roberto <roberto03@gmail.com>]

Hi all,
i know two different packages (among others) are downloadable for math
computing:
octave and octave-forge

i have installed and currently using octave 2.1.69 but what are the
differences with octave-forge??
can i install octave-forge without conflict with octave 2.1? (aptitude
says yes...)
programs in octave 2.1 are compatibles with octave-forge?
or is just octave-forge a bundle of packages usable also from within octave??

thank you very much, any help is appreciated  : )

-- 
roberto
debian sarge, kernel 2.6.8