Extplorer is just what you want it to be - an easy to use file system browser with some nice features built in.
I've had to do a lot of customizing to my site, mostly bits of CSS, and extplorer makes it dead simple. Just like Windows Explorer, browse to a file, open it, edit it, save it, done!
Other features are extremely handy, such as the search function, which helps you find not only files, but content within them. Know the CSS selector but not sure what file it's in? Just do a search for it and extplorer returns a list of all files containing that string.
You can also upload, download, change permissions, diff files, and more right from the toolbar.
With all the tweaks the powers-that-be have wanted for our site, I would have been completely lost without this great tool. Highly recommended!