This is a modification of JWPce, a free, GPL word processor/dictionary written by Glenn Rosenthal back in 1997~2005. There are other free Japanese dictionaries, newer and seemingly more advanced, like Tagaini Jisho, but for some reason I still like JWPce better.
IME support without changing the default system locale. You don't have to use Windows IME to enter Japanese text into JWPce, because it has it's own conversion system, but I still find IME, generally, more convenient. Also, with IME supported, you can use Windows handwriting recognition. Downside: won't work on Windows 95/98/ME anymore (anybody still cares?)
Several modal error dialogs removed (when searching for something less than two kana or romaji characters, when searching for mixed ascii/kana, when exiting). Now, when it can't search, it just doesn't search, without telling you about it and waiting for you to click a button. And when it doesn't have to ask you about saving files on exit, it just exits.
Removed that handy feature with long left mouse click being interpreted as right mouse click, bringing up context menu. Was it made that way for touch interfaces? It was annoying the hell out of me, when I was trying to select some text with a mouse and ooops... sorry, dismiss the context menu and try again without holding your left mouse button for too long.
The entire distribution (14 Mb, with dictionaries and everything).
Source code (430 KB) (Visual Studio 2008 project)