UBCD is one of the oldest LiveCD distributions I know. It seemed to stall in recent years, while other LiveCDs continued to improve and looked like more fancy tech toys to use.
But! It recently got major update to version 5 and it seemed like a great opportunity to revisit and see if disc still worth attention.
What it does
As any diagnostic LiveCD this one boots directly from disc and offers menu with available utilities.
In addition it has Parted Magic bundled, which is LiveCD with plenty of functionality on its own.
All apps are either freeware or open source, with single exception of demo for Astra hardware info utility. There are also no proprietary OS components of any kind, FreeDOS is used in place of MS-DOS.
Disc is built with console in mind and so apps are closer to DOS times rather than to modern graphical interfaces. This means it will work across wide range of hardware but will probably send newbie user in shock. :)
I am on the fence about Parted Magic here. It is great LiveCD, but for specific task. As for me UBCD could use something more generic. There are quite a few Linux distributions around to choose from.
Extensive set of utilities geared towards power users who remember DOS times. Rest risk to scare themselves. :)