"Katana" means something like "samurai sword," if you believe Wikipedia. Apparently, some people collect such things. But the "Katana" I am referring to is something of an nVALT clone. You can download a trial copy from here. It's an interesting application, but it has not been developed now for more than a year, and it does not do everything nVALT does. It also costs $9.99 on the Mac App Store. There is an informative review of Katana here which is to say that this review motivated me to take a look at the application.
One of the things that interested me most was, of course, whether it could do free links like nVALT. It does—sort of. In nVALT, when you enclose a word in double brackets, the program puts that word on the search bar, hitting return creates the note by opening it for writing. nVALT does not seem to care about the case in a note name. Nor does it keep track of the links to renamed notes. (If you rename a note, the old links still point to a now non-existent note. Clicking on the old note just creates a new one.) For anyone used to wiki-functionality, this is a serious drawback. Katana does not use double brackets but the expression <""> to enclose links, like so "<"link">". It does not create a note, if you type a word enclosed in these links. You must create a new note by hand for transforming the expression into a link. There is not even a line in the context menu that would create it. Just like nVALT, Katana does not care about capitalization in note-titles, and, just like nVALT, it does not track tile changes in linked notes. So, if you rename a note, the link will be broken.
Katana only deals with individual text files in a folder (no database option). It supports Markdown. If you save the files on a service like dropbox, its files can be accessed from anywhere, using different kinds of editors. You kind specify the place where files are stored.
It's an interesting application. However, I doubt it has a future. The only way it could thrive in my opinion is, if it improves on nVALT's feature set. Smart links, i.e. links that aren't broken when the target is renamed, would be a good thing. Another thing I would like is the ability to work with different kinds of markup, and not just Markdown. (Italics can be indicated by a pair of "*" or by a Pair of "_". Why not allow other markup, like pairs of "//", etc.)