mac
Adium
- Opensource IM program
Burn
- Way to burn iso or data disks
FreeDMG
- A DMG creator. Free and pretty easy to use
FrostWire
- A LimeWire clone with all the crap ripped out of it
Fugu
- A graphical ssh, scp and sftp client
HandBrake
- Best way to rip DVD to avi,mkv,mov,etc
Lightroom
- A great program for people who do a lot of photo-processing. Not a replacement of Photoshop, but a nice addition
Little Snitch
- A great adaptive firewall to keep programs from "calling home"
MacTheRipper
- Way to rip a DVD to a disk. Play with VLC or burn with Toast
OpenOffice
- Now that the the beta is compiled for OSX it launches faster and doesn't require X11
Senuti
- Copy data from an iPod without being the iTunes owner
Skype
- Make calls over the internet. Can send to landlines for money
Stellarium
- View the nightsky with the constelations
VLC
- Plays just about any file format under the sun. And works with the macbook remote
linux
Inkscape
- The best open source Vector graphics program. Hands down
Straw
- A good stand-alone RSS reader
palm
Arvale
- An RPG. Nice graphics, and **FREE**
Classics
- A collection of games from pda mill.
FreeRange
- A RSS reader. The nice feature is that is stores your feeds online, and you can update them there too.
GooSync
- Keeps your google calendar sync'd up. The free version is a little more limited, but still works.
Kinoma
- A media player to play videos, audio, pictures and "interactive media"
MetrO
- A map software for most of the Metro systems in the world. (Including GTA4)
Mobipocket
- A digital book reader. For mobipocket books.
Opera Mini
- The Opera browser it's better for some of the more "media rich" pages.
Plucker
- A mobile book reader. Supports books from project gutenberg and manybooks.net
pssh
- A port of OpenSSH. Includes pubkey support.
Snails
- A "worms" or "scorched earth" clone.
Tryda
- The yellow pages rolled into an app. Really handy