This is a NEW list of software for Mac OS X that I consider "must-have". The software on this list is software that I use frequently, but the list should be considered dynamic in nature, it may change at anytime. This list is additional software that does not come with the operating system and is updated for Leopard. I had this update sitting around for a while and rather than edit the original post which was geared toward Tiger, I thought I would put up a new post.
Internet and communications
Adium
Adium X is the best multi-protocol instant messenger client, and supports the major transports, such as AIM, ICQ, MSN, Jabber, Yahoo, and more. The interface is very nice and the software is free.,
Firefox
I have used Firefox, well since it was called something else. Firefox has a handful of extensions that keep me using the browser, it is a good web browser but minus the specific extensions I could happily use Safari as well. As matter of fact, I mostly use Safari.
Fugu
Fugu is an open-source FTP and SFTP (SSH Secure File Transfer) client and browser. Fugu has not been updated in a while, but it does everything I need and is free to boot. Transmit is wonderful software, but paying for such an application with Fugu available just seems silly to me.
VLC
VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols. I used it on OS X and Linux and it even streamed Alex's ogg vorbis stream on the Mac when all others failed.
Audacity
Audacity is a free, open source software for recording and editing sounds in Mac OS X, Linux and other operating systems. I use this application to record my side of the podcasts, which I then export to FLAC format. FLAC stands for Free Lossless Audio Codec, an audio format similar to MP3, but lossless, meaning that audio is compressed in FLAC without any loss in quality.
Flickr Uploadr
The Flickr Uploadr provided free from Flickr is all I need to get my photos to Flickr. I drag and drop from iPhoto to the Flickr Uploadr where I can apply tags, descriptions and even create sets or add photos to existing sets. Recent releases have improved functionality, so if you have not checked it out in a while you might want to.
Gimp
GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring. I am in no way a graphic artist, GIMP serves this amateurs needs.
Productivity
NeoOffice
NeoOffice is a Mac-only port of OpenOffice.Org. It is a free and excellent office suite that meets all my office suite needs, and enables you to work with Microsoft generated office documents too. If you are using OpenOffice on the Mac, NeoOffice is what you should be using.
BuffSched
Buffsched is a command line scheduling application I wrote in shell script and is currently compatiable with Mac OS X, Linux, AIX, Solaris and HP-UX. A simple text file holds all your scheduled appointments and ignores any entries that are not in the BuffSched format. This is so you can keep a todo list, an address book and any other information you deem useful in the text file. I carry mine on a thumb drive so I can access and change my schedule at work and at home. I mostly use BuffSched on my servers as a replacement for Message of the Day and include the program in users default profile. I can easily keep users posted of scheduled maintenance with BuffSched.
MacVim
MacVim is a port of the text editor Vim to Mac OS X that is meant to look better and integrate more seamlessly with the Mac than the existing Carbon port. After trying other Mac Text editors, I am back to Vim. The bottom line is that I can install Vim on all the other operating systems I use and it works the same. Being an old UNIX jockey I am familiar with vi on the command line. There can be no argument, Vim is the best!
svnX
SvnX is an open source GUI for most features of the svn client binary. SvnX allows you to browse your working copies, spot changes and operate on them. SvnX can also browse logs and revisions of your repositories. I have been working with a Subversion server hosted on AIX and svnX has worked wonderfully.
TrueCrypt
TrueCrypt is free open-source disk encryption software for Windows, Mac OS X and Linux. I use TrueCrypt to encrypt my thumbdrives and with TrueCrypt I can access the drives from my employers Windows machine or from any of my Linux or Mac computers. I needed a solution that I could use with all the major desktop operating systems, TrueCrypt is that solution. TrueCrypt is an awesome encryption solution even if you do not use a Mac.
VMware Fusion
I purchased VMware Fusion during the beta phase. VMware Fusion runs the only Windows installation found in my home and is useful for trying different distributions of Linux. Vmware Fusion has been running Windows Vista Ultimate edition on my Macbook just fine. Though I confess that I really have not had a reason to boot my virtual Windows guest in months.