Mac only: Many users have been unhappy with OS X's Finder for a while, wishing for tabs, fixes for hidden file annoyances, and other conveniences. TotalFinder is a plug-in containing all this and more, creating a Finder worthy of a power user.
We've all been itching for new features in Finder, and the latest upgrade to Snow Leopard did little to help that on the surface — but its rewriting in Cocoa has opened Finder up to all the possibilities of SIMBL plugins, which TotalFinder has taken advantage of. The biggest upside to this approach is that, unlike current Finder-replacement favourite PathFinder, TotalFinder integrates into the existing Finder so you don't have another application to launch. Also, it's free (albeit less feature-rich).
Some of the highlights include making Finder accessible at all times with just a hotkey, and some hidden features that most of you Finder power users have probably already implemented, like showing hidden files. However, it adds to this by redirecting those annoying .DS_Store files to another folder, rather ingeniously — they'll still be accessible by Finder, but never again will they clutter up every Finder window you open.
Possibly the coolest and most wished-for feature TotalFinder adds, though, is tabbed browsing. The plug-in adds tabs to the title bar — similar to Chrome's (OK, they're exactly like Chrome's) — to save on some of that oh-so-precious screen real estate. Simple, but a huge boon to anyone who spends a lot of time in the app.
The biggest downside to TotalFinder is that it's still in alpha stage. In fact, it's more unstable than your average alpha — if there were such thing as super alpha, TotalFinder would certainly fall into that category. So make sure you have your Time Machine backup prepared just in case, and be forewarned! But if you back up religiously and love the thrill of over-tweaking your computer with unstable software, have at it. If you don't like it, there's an uninstall script that will remove it completely from your computer. Also, because it's in such early stages, the developers have a lot of things planned for the future — so, in theory, TotalFinder won't always be the unstable, feature-minimal upgrade it is now — god willing, we may all have a nice PathFinder replacement on our hands one day.
TotalFinder is a free download, Mac OS X 10.6 only.
Update: It turns out that the plugin is likely only going to be free until the developer releases a beta version - but at least you can try it out until then, and worry about it when it turns into a pay app.