Apple advertised that Mac OS X 10.4 Tiger had over 150 new and improved features, including:

• Spotlight — Spotlight is a full-text and metadata search engine that can search everything on one's Mac, including Microsoft Word documents, iCal calendars and Address Book contact cards. The feature is also used to build the concept of 'smart folders' into the Finder. Spotlight will index files as they are saved, so they can be quickly and easily found through a search-as-you-type box in the menu bar. As a side-effect, it adds hidden folders and indexing files to removable media like USB flash drives.
• iChat AV — The new iChat AV 3.0 in Mac OS X 10.4 Tiger supports up to four participants in a video conference and ten participants in an audio conference. It also now supports communication using the XMPP protocol. An XMPP server called iChat Server is included on Mac OS X 10.4 Tiger Server.
• Safari RSS — The new Safari 2.0 web browser in Mac OS X 10.4 Tiger featured a built-in reader for RSS and Atom web syndication that can be accessed easily from an RSS button in the address bar of the web browser window. An updated version of Safari, included as part of the free Mac OS X 10.4.3 Tiger update, can also pass the Acid2 web standards test.
• Mail 2 — The new version of Mail.app email client included in Mac OS X 10.4 Tiger featured an updated interface, "Smart Mailboxes", which utilizes the Spotlight search system, parental controls, as well as several other features.
• Automator — A scripting tool to link applications together to form complex automated workflows (written in AppleScript, Cocoa, or both). Automator came with a complete library of actions for several applications that can be used together to make a Workflow.
• VoiceOver — screen reader interface similar to Jaws for Windows and other Windows screen readers that offers the blind and visually impaired user keyboard control and spoken English descriptions of what is happening on screen. VoiceOver enables users with visual impairment to use applications via keyboard commands. VoiceOver is capable of reading aloud the contents of files including web pages, mail messages and word processing files. Complete keyboard navigation lets the user control the computer with the keyboard rather than the mouse, a menu is displayed in a window showing all the available keyboard commands that can be used.
• A complete built-in Dictionary/Thesaurus based on the New Oxford American Dictionary, Second Edition, accessible through an application, Dictionary, a Dashboard widget, and as a system-wide command (see below).
• .Mac syncing — Though this was not a new feature, .Mac syncing in Tiger is much improved over Panther. Syncing tasks in Tiger are now accomplished through the .Mac system preferences pane rather than the iSync application.
• QuickTime 7 — A new version of Apple's multimedia software has support for the new H.264/AVC codec, which offers better quality and scalability than other video codecs. This new codec is used by iChat AV for clearer video conferencing. New classes within Cocoa provide full access to QuickTime for Cocoa application developers. The new QuickTime 7 player application bundled with Tiger now includes more advanced audio and video controls as well as a more detailed Information dialog, and the new player has been rebuilt using Apple's Cocoa API to take advantage of the new technologies more easily.
• New Unix features — New versions of cp, mv, and rsync that support files with resource forks. Command-line support for features such as the above-mentioned Spotlight is also included.
• Xcode 2.0 — Xcode 2.0, Apple's Cocoa development tool now includes visual modelling, an integrated Apple Reference Library and graphical remote debugging.

• Dashboard — The Dashboard is a new mini-applications layer based on HTML, CSS, and JavaScript, which returns the desk accessories concept to Mac OS. These accessories are known as widgets. It comes with several widgets such as Weather, World Clock, Unit Converter, Dictionary/Thesaurus, and others (full list). More are available to download for free online. Its similarity to the Konfabulator application caused some criticism.
• Automator — Automator uses workflows to process repetitive tasks automatically
• Grapher — Grapher is a new application capable of creating 2D and 3D graphs similar to those of Graphing Calculator.
• Dictionary — A dictionary and thesaurus program that uses the New Oxford American Dictionary. It has a fast GUI for displaying the Dictionary, and allows the user to search the dictionary with Spotlight, to print definitions, and to copy and paste text into documents. Dictionary also provides a Dictionary service in the Application menu, and Cocoa and WebKit provide a global keyboard shortcut (ctrl-⌘-D by default) for all applications that display text with them. Its use was furthered in Mac OS X Leopard by providing definitions from Wikipedia. The Dictionary application is a more feature-filled version of the Dictionary widget.
• Quartz Composer — Quartz Composer is a development tool for processing and rendering graphical data.
• AU Lab — AU Lab is a developer application for testing and mixing Audio Units.

• An upgraded kernel with optimized kernel resource locking and access control lists, and with support for 64-bit userland address spaces on machines with 64-bit processors.
• An updated libSystem with both 32-bit and 64-bit versions; combined with the aforementioned kernel change, this allows individual applications to address more than 4 GB of memory when run on 64-bit processors, although an application using Apple libraries or frameworks other than libSystem would need to have two processes, one running the 64-bit code and one running the code that requires other libraries and frameworks.
• A new startup daemon called launchd that allows for faster booting.
• The printing dialog in Tiger now features a drop down menu for creating PDFs, sending PDFs to Mail, and other PDF related actions. However, the user interface was criticized for creating a hybrid UI element that looks like a plain button but acts like a pop-up menu. This is one of only three places in the entire Mac OS X interface where such an element appears.
• Dock menus now have menu items to open an application at login, or to remove the icon from the dock.
• The Window menu in the Finder now features a "Cycle Through Windows" menu item.
• The Get Info window for items in the Finder now includes a "More Info" section that includes Spotlight information tags such as Image Height & Width, when the file was last opened, and where the file originated.
• Early development of resolution independence. Apple notes that this will be a user-level feature in a future version of Mac OS X. Among the changes, the maximum size of icons was increased to 256x256. However, the Finder does not yet support this size.

• Core Image: A graphics processing API that allows programmers to leverage programmable GPUs for fast image processing for special effects and image correction tools. Some of the included Image Units are Blur, Color Blending, Generator Filters, Distortion Filters, Geometry Filters, and Halftone features.
• Core Data: A data persistence API that makes it easier for developers to handle structured data in their applications. Core Data provides undo, redo, and save functions for developers without them having to write any code.
• Core Video: A video graphics API that leverages Core Image to provide real-time video processing. Apple's Motion real-time video effects program takes advantage of Core Video in Tiger. Core Video lets developers easily integrate real-time video effects and processing into their applications.
• Core Audio: Integrates a range of audio functionality directly into the operating system.

In addition to these APIs, Tiger introduces a new window theme, often described as 'Unified'. A variation on the standard, non-brushed metal theme used since the introduction of Mac OS X, this theme integrates the title bar and the toolbar of a window. A prominent example of an application that utilizes this theme is Mail.

Tiger is also the first version of Mac OS X to include the "Zoom" screen magnifier functionality.

At Apple's 2005 Worldwide Developers Conference, CEO Steve Jobs announced that the company would begin selling Mac computers with Intel x86 processors in 2006. To allow developers to begin producing software for these Intel-based Macs, Apple made available a prototype Intel-based Mac ("Developer Transition Kit") that included a version of Mac OS X v10.4.1 compiled to run on x86 processors.

This build included Apple's Rosetta compatibility layer — a translation process that allows x86-based Macs to run software built only for PowerPC, with a moderate performance penalty. This is contrasted with the contemporary Mac OS 9 Classic mode, which used comparably larger amounts of system resources.

Soon after the Developer Transition Kits began shipping, copies of Tiger x86 were leaked onto file sharing networks. Although Apple had implemented a Trusted Computing digital rights management scheme in the transition hardware and OS in an attempt to stop people installing Tiger x86 on non-Apple PCs, the OSx86 project soon managed to remove this restriction. As Apple released each update with newer safeguards to prevent its use on non-Apple hardware, unofficially modified versions were released that circumvented Apple's safeguards. However, with the release of 10.4.5, 10.4.6, and 10.4.7 the unofficially modified versions continued to use the kernel from 10.4.4 because later kernels have hardware locks and depend heavily on EFI. By late 2006, the 10.4.8 kernel had been cracked.

At MacWorld San Francisco 2006, Jobs announced the immediate availability of Mac OS X v10.4.4, the first publicly available release of Tiger compiled for both PowerPC- and Intel x86-based machines. This version was the first version, other than the version provided with the Developer Transition Kits, to include Rosetta.