TeuS

sum those less obvious alternatives up!

MSN/AIM/...: GAIM

Audio: XMMS + MPEG patch. there are some legal problems so you can't play MPEG files (mp3's), but the unofficial patch fixes it (google it!)

automatic update managers: YUM or APT (yum handles the dependencies better). very ease: one command lets all packages be updated or install a new one!
http://apt.freshrpms.net

RichBa5tard

Gentoo doesn't need a third party auto update manager, emerge is one of it's building stones. : )

Video Editing (virtual dub/...): avidemux4
Browsers: Mozilla (incl irc, mail client) / Firebird (excl irc, mail)
remote login: xdmcp capable progs, eg GDM (gnome)
Office apps: OpenOffice, Abiworld, KOffice
File manager (my computer/...): Nautilus
Proxy server: squid
FTP server: vsftpd
Windows compatible file server: samba
Basic W2000 server capabilities (eg roaming profiles): samba 3.x
image editing: gimp 2.x
download manager: prozilla, d4x
movie player: mplayer (great app! plays realmedia, all divx, xvid, mpeg, wma, asf, ...)

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HTPC (mac osx): Mac Mini | Core Duo 1.6Ghz | 2GB DDR2 | 26\" TFT
Development (mac osx): Macbook | Core 2 2.0Ghz | 4GB DDR2 | 250GB HD
Games (win xp): E2160 @ 2.4Ghz | HD3850 OC | Asrock 4coredual-vsta | 2GB DDR2