Although its developers warn that this is an early beta release
still in heavy development, this project still bears watching:
MrProject is a GNOME-based project manager licensed under the GPL.
From the status report:
"What does it do so far? MrProject has a long way to go
before it can compete for real with available commercial project
management applications. The basic infrastructure is there, and now
all we have to do is fill in the blanks. If you feel that this is
something you want to help out with, please join the mailing list
or contact us for any questions you might have."