software for OS X

Some of this software may be incompatible with versions of OS X later than 10.4 (Tiger). In many ways, OS X has not improved since then, and I no longer use it anyway (but I do update this list occasionally).

$ = requires key for unimpeded operation

repositories

MacUpdate
reviews and links to popular OS X software updates
MacPorts | Fink

package management systems for open-source unix software ported to OS X; these may seem easier than compiling from source but one remains dependent upon the package maintainers, and I've come to generally use them as a last resort

For the command-line, see Unix software...

utilities

LaunchBar
$ : very useful, quick, configurable keyboard access to find/open/manipulate files/programs; also has multiple clipboard/pasteboard support (free alternative: Quicksilver)
OnMyCommandCM
make your own system-wide contextual menu commands
TextExtras
installs a menu of useful text-handling commands for Cocoa applications
DEVON technologies
useful service modules (CalcService, WordService), and EasyFind
MenuMeters
CPU/memory/disk/network info in menubar
GrandPerspective
tree map of disk usage
DiskWarrior
$ : repairs HFS+ volumes (where others fail or make matters worse)

network

Little Snitch
$ : internal firewall (for detection/prevention of network connections from the inside out)
CyberDuck
FTP and SFTP client
NetNewsWire
$ : RSS/RDF client (free "Lite" version also available)
Meteorologist
current weather information and forecasts in dock or menu bar (supports cities around the world)

programming

Hammerspoon
Lua script interface to various system services/components
HexEdit
hexadecimal file editor

media (audio/video/&c.)

VLC | mpv
multimedia players for various audio and video formats including most Windows Media files

unfiled

UnicodeChecker
explore and convert Unicode