Ubuntu Linux is designed for Human beings. It tends to be as easy as possible for all of them and to make things just work. A similar contender on this concept but in the web browser/e-mail environment is Opera. Sadly it is not open source but it is freely available to anyone and on many platforms and languages.
Opera features many enhancement regarding accessibility (and are/were pioneer in many of this area). They have integrated into their browser things like mouse gesture, voice control and many UI improvements (some were adapted in other major software) including: tabs, sessions, zoom and private data management.
It seems as if Opera has always tried to make their software more ergonomic with each new release. Something that was not really considered seriously until recently by the contenders.