Quicksilver is a utility available for Mac OS X. Its function is analogous to that of a command line interface, any Mac OS 1-derived GUI, or any other way of interacting with a computer: it provides a scalable way to access, change, and organize data on your computer. It is developed by Blacktree, and Quicksilver and its source can be downloaded from http://www.quicksilver.blacktree.com. At the time of this writing, it is at version β49. Because of the depth and breadth of its functionality, it will not run on any operating system other than 10.4 (Tiger), although β35 for 10.3 (Panther) is still available.
From blacktree.com:
In the end, Quicksilver has one very important effect: the effort of frequent tasks fades into the background and you are able to act without thinking. After an adaptation period, Quicksilver becomes an extension of yourself; the process fades away leaving only the results.
A properly configured Quicksilver will make you understand and use your computer on a level that was previously only possible for hackers in cheesy movies. I am not exaggerating. Quicksilver is so powerful that when you attempt to explain it to your friends, you will be at a loss for words. It makes menial tasks trivial, it exposes functionality in a way that programs and the OS can't easily do, and it makes the interconnectedness of programs and data in OS X into something that makes a nerd's heartstrings quiver.
When you first get Quicksilver, you will probably use it as a file launcher. This is fine. It can do this very powerfully and effectively. When setting up Quicksilver, you configure "catalogs" — basically, sources of data. These can be volumes, directories, and (once you start using plugins) more interesting things. We'll get to that later. When you configure directories, Quicksilver gives you (among other things) the option of specifying the subdirectory depth to which it indexes data, the ability to restrict the indexing to specified file types, and the ability to remove any indexed item from the catalog.
Once you have the directories you want to access configured and indexed, opening Quicksilver's Command Window (which can be done by a hotkey, by opening Quicksilver from the hard drive or any file launching system, or other fashions, depending on your plugin configuration) and beginning to type will present you with Quicksilver's best guess as to what you want to open. This will change over time as you use Quicksilver, as the utility maintains a constantly-evolving dictionary of what you have typed in the past in order to match commonly-typed inputs with the data you want. It is important to note that Quicksilver is performing subsequence matching for what you type: if you want to open, say, Adobe Photoshop, "adobe" can be just as effective as "aphoto", or, in my case, "ps." When you first start using Quicksilver, it won't be amazing at this. You will have to train it. The easiest way to do this is simply to use it frequently. It will start to build up its dictionaries. You can also locate anything with Quicksilver (or find it using the Finder and press Command-Escape, which will open the Command Window with that file selected) and assign it the abbreviation of your choice. This brings us neatly to the Action Pane.
Actions are the heart and soul of Quicksilver. When you find a file, you can click into the Action Pane (or tab to it, or space-bar to it, or simply start typing in capital letters, depending on how you have configured Quicksilver) and find an Action. Quicksilver has many, many Actions. With plugins, my Quicksilver currently has 233 Actions in 11 categories. Limiting myself to File and Folder Actions for the time being, these range from Open, Open With…, Raise Priority (for a running process), Compress (using any of five common compression techniques), Email To…, Get File Path, as well as any action from the Mac OS' Services menu, which are automatically imported into Quicksilver with the appropriate plugin.
Some Actions require a third datum: these range from a folder to move something to, a program to send it to, a line of text to alter it with, a contact from your Address Book, and many others. When these are needed, a third pane appears. When they are not, it is hidden. Think of it as an argument to the Action.
If this sounds confusing, it should be. It will become very clear as soon as you use Quicksilver. Quicksilver is more adaptive, more configurable, and more intuitive than anything else you have ever used. You can restrict it to be very weak or expand it to be so powerful that the Finder, Dock, Menubar, and most other parts of the Mac OS GUI are unnecessary fluff. Let me demonstrate this by explaining plugins.
Quicksilver has many plugins. Some give Quicksilver the ability to interact with specific programs: the Address Book plugin lets you access contacts (or any field within a contact: I can type in a friend's name and send their phone number to Skype, or their e-mail address to Thunderbird, or simply dump the contents of a field into whatever is the active program); the Terminal plugin adds Actions related to the command-line; the Transmit plugin gives me FTP and SSH actions through the program Transmit. Some add useful features to Quicksilver: the Extra Scripts plugin gives you Applescripts to control shutdown and sleep, open keyboard utilities, find your IP address, and more; the Growl plugin makes Quicksilver Growl-compatible (check out http://www.growl.info for information on Growl, another very cool utility); the Mouse Triggers plugin makes Triggers (basically stored Quicksilver commands) activatable with the corners and sides of the screen and any number of modifier keys. Some plugins give you a new appearance to Quicksilver: you can have the Command Window have a number of different shapes and layouts, be very compact and roll down to cover the Menubar, or mimic the look of Spotlight (which, interestingly enough, complements Quicksilver instead of being superseded by it). Finding and installing plugins is integrated within Quicksilver: one of the panes in its Preferences lists all known plugins, and they are automatically downloaded, installed, activated, deactivated, and reactivated by checkboxes.
It is quite simple to develop plugins: Quicksilver has a large and helpful developer community attached to itself. Plugins can be written in Objective-C or PyObjC, an extension of Python which gives it those parts of Objective-C necessary to interact with other heavily Cocoa-oriented programs. If you don't know either of these, Quicksilver can be quickly and effectively extended with Applescripts.
Quicksilver has many other features I haven't mentioned here. You can develop a library of triggers, which are macros that can perform any Quicksilver command, be layered, and get activated through keyboard combinations, a variety of mouse actions, or even gestures. You can stack data and perform mass actions on them; you can quickly and easily navigate layers of subdirectories, whether on the hard drive or metaphorically in, say, your music library; you can locate a program and press right to access program data that a plugin has taught Quicksilver about (such as locating the Address Book and pressing right to access contacts, locating iTunes and pressing right to be given the choice of navigating iPod-style through artists, songs, playlists, and others); you can locate a program and press option-right to access package contents (if you don't understand that, don't worry). Of course, Quicksilver is utterly beautiful. It uses all of the silly little effects that Core Graphics gives to developers: panes and menus slide, spin, fade, and change in ways that another operating system simply would not be able to handle. None of this interferes with the utility of Quicksilver: it's just nice to know that the most useful program on your computer is also the best-looking.
I cannot recommend Quicksilver highly enough. It took me the better part of a year to become a power user with it, but using a computer without it now feels clunky and awkward. It embodies everything that is right about the Mac OS and wrong about Windows. Quicksilver knows what I like, and brings it to me the way I want it. It takes full advantage of the interactions between programs that are coming to the fore in OS X. It looks fantastic, runs cleanly, and makes plenty of other programs and technologies obsolete. It is very cool to know that I can start typing, and my favorite programs will appear, that if I type in a URL, I can just Open it and Quicksilver will know which program to handle it with (or I can force that URL into any other program that thinks it knows how to handle it), that if want somebody's work fax number, it will take about ten keystrokes to find it. If you have a Mac running OS 10.4, you owe it to yourself to download and install Quicksilver. It is the future of interacting with your computer.
To find out more about Quicksilver and its use, explore the following: