Depeche View Lite (free) begins with an interesting concept: a powerful tool for searching across hundreds or even thousands of text files with a single click. It loads an entire directory, including subdirectories, of text into RAM (it is limited to about 1GB because it is a 32-bit program), and then can search this block amazingly fast. Unfortunately, this functionality is hidden behind one of the strangest interfaces I've seen since the mid-1980s.
In the earliest days of GUIs on personal computers, software vendors would take their old text-mode software, wrap a simple frame around it with a default menu bar, and sell it as a graphical upgrade. Depeche View hearkens back to those days, with an interface that ignores just about every Windows convention there is, and a menu bar which often does nothing but display the necessary keyboard commands to perform the function you selected. You must then enter these commands manually.
To pick one simple example, how do you select two words to use as a string to search for? You hit <CTRL>, release it, hit it again, don't release it, click the left mouse button, drag over the text, then release the mouse button, then release control. The documentation for Depeche View calls this the "one and a half click" method. I call it migraine-inducing. The entire interface follows this pattern of mixing <CTRL>, <SHIFT>, and mouse clicks in ways no Windows program ever has before. Even Windows ports of *nix stalwarts like EMACS and vi throw more bones to following UI guidelines. In the strangest twist of all, Depeche View runs under Linux only in a Windows emulator. Yes, we have here a program that doesn't use any part of the Windows environment and yet needs a Windows emulator to run.
There are some things Depeche View does well, if you can figure out how. First, as promised, it is fast. It loads files quickly, and scrolling is extremely rapid, if you can figure out how to get the totally non-standard "scroll bar" to work, or just use CTRL-SHIFT-END and CTRL-PAGE-UP and the like to jump around.
Depeche View's keyboard commands are not entirely unintuitive, once you accept the fact there's no other way to do anything and that the menu bar is a cruel, cruel, joke. But if I want vi--and sometimes I do--I know where to find it.
If you find a word you're looking for, a right-click in Depeche View opens a second view focused on that word; another useful option is that you can filter that view by clicking on the odd-looking "F" button, which will show you just lines that contain that word.
For users who need to analyze directory trees filled with text files, Depeche View offers the ability to filter paths; you can select, for example, a directory tree which contains many sub-directories with log files, and then search only the text files which are in those directories which include the name of a particular server. There are quite a few useful features here, none of which mandate the use of a non-standard interface. Having powerful keyboard controls for experienced users is a wonderful thing; having no other options a quarter century after the Macintosh brought the GUI to the desktop is madness.
Depeche View's central concept of merging all inputs into an in-memory file and then searching it is distinctive, and this is a point in its favor. However, many search-related tasks can be accomplished via more traditional tools, from grep to Google Desktop, and most programming environments have built-in source code search tools as well. Depeche View has a great idea at its core, but imposes a usability tax that may be too onerous for most.
Depeche View Lite is free, and there is a thirty-day demo of Depeche View Pro, which includes a file editor and some other advanced features. If the feature set hits your personal needs, it is probably worth checking out to see if you can adjust to the interface oddities.