I thought I would run down some of the software that I have been using lately. Some that I just started using, some that I have been using for quite some time. My main computer is a macbook pro, so all of this software is going to be for OS X Leopard, though some of it is available on other platforms.
Gizmo Project - This is available for many platforms linux, windows, and some mobile phones. It is a great VOIP option, however maybe not the best under low bandwidth conditions.
Grand Central- Not software, but a service recently bought by Google. If you can an invite, which I did within a couple of days, then it is awesome with your gizmo project phone. Grand Central rings multiple phones when some calls your number, with many different options and settings. But the really awesome thing is that it will ring your gizmo project phone. thus give your voip phone a free number for incoming calls. what about outbound? well just add the person to your contact list at Grand Central then from the website, click call. Grand Central will ring your gizmo project phone and once you pick up connect you with the other party. as simple as that, free calls. yes indeedy free.
Last.fm - Service and software, use the last.fm client to track your music plays and use the last.fm website to recommend music and let you keep in touch with your friends music tastes.
Of course there are the standard Mac apps that are a must: Vmware, Adium, Transmit (though right now I’m using a trail of Forklift, and I’m a bit torn on which is better.), and VLC for those videos that quicktime just won’t play.