Sure, Safari is its own app, but new OS X versions tend to bring new versions of Safari, and Mavericks is no exception. Safari 7 offers a new sidebar, plug-in management, a redesigned Top Sites page, performance improvements, and a new feature designed to remember your passwords without compromising security.
Sidebar full of links
The Mountain Lion version of Safari offered three features accessible via buttons on the far left side of what it called the Bookmarks Bar: Reading List, Bookmarks, and Top Sites. Safari 7's rechristened Favorites Bar features only two: Sidebar (which somewhat confusingly still uses the Bookmarks icon of an open book) and Top Sites.
The new Sidebar is the new home of Bookmarks, Reading List, and the new Shared Links feature. It's a gray bar (minimum width: 300 pixels) that lives on the left side of the browser window. To open it, click the book-shaped Sidebar icon on the toolbar, or choose Show Bookmarks Sidebar, Show Reading List Sidebar, or Show Shared Links Sidebar from the View menu. (There are also keyboard shortcuts--Command-Control followed by 1, 2, and 3, respectively. You can toggle the Sidebar on and off by pressing Command-Shift-L.)
In previous versions of Safari, going to the Bookmarks view replaced the contents of your browser window with a bookmark editor, where you could drag and drop bookmarks and rename them. That window is still there if you choose Show Bookmarks from the Bookmarks menu, though it's now a hierarchical view full of folders, instead of the weird old interface where different folders were in a separate sidebar of their own. If you want to do organizational work on your bookmarks, this is still where you need to go.
But a new Bookmarks tab in the Sidebar gives you one-click access to your bookmarks. Just click a bookmark in the Sidebar, and Safari loads that page on the right side of the same window. Click a folder to show or hide its contents. You can drag items around and edit them by Control-clicking them and choosing Rename Bookmark or Edit Address. You can change the name by clicking and holding on it for a few seconds. There's also a search box above the top of the list, if you need to find a specific bookmark, and a plus (+) button at the bottom to create a new folder.
Sidebar, your honor?
The new Bookmarks tab seems like a nice approach for people who want one-click access to more bookmarks than will fit on the Favorites Bar, or as an alternative for people who simply prefer the Sidebar to the Favorites Bar. And it's a much more accessible way to organize your bookmarks than the old view.
The second tab in the Sidebar is Reading List, and it's not that different from the Mountain Lion version. This is still the place where you can collect webpages that you want to read at a later time, even if you're offline. The big difference in Safari 7 is that the Reading List scrolls endlessly. Once you're at the bottom of a Reading List story, just keep scrolling down to go to the next story in the list.
In previous iterations of Safari, there were toolbar buttons for adding stories to your Reading List and links to your Bookmarks. In Mavericks, Safari no longer provides those buttons. Instead, there's a big plus (+) button integrated in the address and search bar, just to the left of the page's URL. Click the plus button to add the page you're on to Reading List; click and hold to see a menu of options, including adding the page to Reading List or Top Sites, or filing it as a bookmark in any of your bookmark folders.
The third (and most interesting) addition to the Sidebar is the Shared Links tab. Once you've logged in to a Twitter or LinkedIn account via the Internet Accounts (formerly Mail, Contacts and Calendars) preference pane, any posts that contain hyperlinks appear in the Shared Links list. If you use your Twitter stream as a replacement for RSS feeds, Shared Links offers a concentrated burst of Twitter linkage that eliminates the middleman.
The Shared Links sidebar displays posts with the most recent item at the top. They aren't bare links, either--you see the avatar of the person who posted the link, his or her name, an icon representing the service the post came from (it just supports Twitter or LinkedIn at this point), and the text of the post itself. Click anywhere on the post to display it in the browser window, and, as in Reading List, if you keep scrolling to the bottom of the story, you can scroll right on to the next story in the list.
Share and share a link
The new Shared Links section of the Sidebar lets you browse links from people you follow on Twitter or LinkedIn.
As you read a story, the original post that spawned it remains at the top of the screen, so you can quickly find the answer to the question "Which one of my friends thought this was worth tweeting about?" There's also a Retweet button, so if you think the story is interesting, you can pass it on.
Next to the Sidebar button is the Top Sites button, and of course there's a new version of the Top Sites interface, which presents you with six or 12 or 24 of your favorite sites in a grid. (It's now a proper Hollywood Squares--style grid, with none of the curved-wall effects of the previous iteration of Top Sites.) The look seems more modern and allows you to reorganize your Top Sites items via drag and drop.
Faster, lighter, safer
Apple also says that Safari has a bunch of new under-the-hood features that improve speed, reliability, and security. Separate pages run in separate processes, it has improved memory management, and it takes advantage of Mavericks' power-saving features to run more efficiently.
One major source of stability, speed, and energy-consumption issues in Safari isn't actually Safari itself--it's browser plug-ins such as Adobe Flash. Third-party tools like ClickToPlugin have long let users manage whether webpages can load those plug-ins, and in Mavericks, Safari has a similar feature built right in.
Plug in, tune out
The feature lives in the Security tab of Safari's preferences window, under the Manage Website Settings button. From here you can see every browser plug-in your system is using and a list of sites that have loaded each one. You can turn access on and off on a per-site basis, as well as set a default for what happens on your first visit to a website that's trying to load a plug-in. For example, you can set YouTube to always load Flash, but all other sites to block Flash on first load.
Safari now also has a Power Saver feature that will sometimes prevent plug-ins from loading until you click, emulating ClickToPlugin's approach. Safari should really go further, though, and allow an intermediate option in Manage Website Settings, so that you can set certain plug-ins to load on a click.
And when Safari is blocking a plug-in, the browser replaces the space occupied by the plug-in with an empty box. This happens because Safari is reporting to the server that it has the plug-in, but doesn't show the content. Some sites offer non-Flash equivalents if a device (such as an iPhone or iPad) doesn't have Flash, but Safari doesn't see those if Flash is installed but disabled.
iCloud Keychain arrives
iCloud Keychain stores your passwords, credit card numbers, and personal contact information, and syncs them between devices running Mavericks or iOS 7. Since it's all synced via iCloud, it should always be up to date, so if you save a password on your Mac, it'll be there when you next visit that site on your iPad. That's pretty cool. (This is an optional feature--nobody's forcing you to put your stuff in the cloud. You turn it on by checking the Keychain box in the iCloud preference pane.)
This approach has some major advantages over utilities like 1Password, since it integrates the password feature directly in the browser on the Mac, rather than via an extension.
Safari can now not only remember your website passwords, but even suggest more secure ones (which it will remember and sync for you).
Safari's been able to remember your usernames and passwords for ages now (only the syncing part is new), but it will now also suggest a random password when you're prompted to create one. (This is good, because simple passwords are insecure.) Then Safari will save the random password in the keychain, so you never have to remember it. Safari can also remember your credit card information and automatically fill it in (well, most of it--it won't store your card's security code, which Apple says "is in accordance with industry practice") when you want to buy something.
If you're concerned that other people will have access to your passwords and credit card numbers, you need to set your Mac to lock when it goes to sleep or when the screen saver activates, and set a very low time-out period before that happens. You can set the Mac's normal keychain to lock after a period of inactivity, but you can't set iCloud Keychain to lock automatically.