(!) Note that even though most planned features are in place and I myself find it highly stable and reliable in everyday use, Qalculate! definitely needs more testing and no guarantees whatsoever are given :-o
With that said, you are welcome to download the latest version of Qalculate! and report any bugs you find. libqalculate is required for all the other packages.
Qalculate version 0.9.7 (2010-01-06)here.
There are also a some RPM packages available. Look here for Fedora, and here for other distributions.
KDE GUI requirements:
GTK+ GUI requirements:
Text interface requirements:
Qalculate! Bases, Currency, and Units requirements: