Following an inline link on Wikipedia I know what to expect, basically a definition of the linked concept. External links on the other hand I consider more like footnotes at the end of a book chapter or an article. Regarding inline links all over have a look at the 1999 website a-blast.org / assoziations-blaster.de
On GNU/Linux Thunderbird ist my favourite GUI mail client, offering support for a variety of standards, including e.g. CalDAV (CardDAV in Beta), OpenPGP and S/MIME.
Not sure whether Chat should be part of it, currently offering Google Talk, IRC, Odnoklassniki, and XMPP (Twitter finally gone). Support for Usenet News is appreciated, though I enjoy Pan.
On GNU/Linux I thus consider GNOME Evolution as best alternative. (Haven't looked at the KDE suite for some time with Akonadi being too heavy last time I tried it on my simple machine.) Neither Claws, Geary, Sylpheed, or others offer such broad support, although those are very nice GUI clients.