Download openproj from http://sourceforge.net/projects/openproj/
Yes, you can only download the rpm file. But you can also install it in Ubuntu via alien.
sudo apt-get install alien
sudo alien -i openproj.rpm
Then run it.
you will got these errors
Your Java vendor is "Oracle Corporation". To run OpenProj, you need the Sun Java implementation.
The auto-detected Java Runtime used is..
Open $HOME/.openproj/run.conf and Change
JAVA_OPTS="-Xms128m -Xmx768m"
TO
JAVA_OPTS="-Djava.vendor=Sun -Xms128m -Xmx768m"
Then run it again, it works fine.
Have fun with Ubuntu!