Debian is quite modern and it does support the new Glibc2 library system. Like Redhat, Debian is reported to be constantly updated and well supported. Many people argue that Debian is even better updated than Redhat though they are considerably slower to release new distributions compared to the other vendors. They initially pulled ahead of the pack with a better installation program and auto-installing hardware modules but everyone caught up pretty quick. Caldera is understood to have the easiest installation program of ALL the distributions.
Caldera differentiates itself by trying to meet the needs of the corporate market.
For example, they have completed a port of Novell's NDS directory services to Linux. I had previously tried their 5.x version but there was so much embedded German text in it, it bothered me so I gave up on it. I recently installed version 6.0 and it seems much better. Its installation program is pretty good though I think Redhat's is somewhat better. But, SuSE has a nice configuration tool called YaST and they were one of the first to come with the KDE window manager.