Markdown editors are all pretty much the same: simple text with a handful of markdown symbols to control formatting. What distinguished SmartDown was that it also offered "folding" - the ability to "collapse" or conceal text under a "#" heading.
In short, it was a clean, fast, quickly learned writing application that allowed for the creation and manipulation of complex documents. At the end, the text could be exported or copied as html or rtf.
There were a few oddities in SmartDown: changing preferences required the direct editing of a configuration file. It showed on-screen symbols for soft returns (which could be toggled, but again required config file editing). Minimizing the app moved it to the lower right taskbar area, rather than the more typical task bar icon. Hitting Home and End took you to the beginning and end of a paragraph rather than the onscreen line.
But I liked it. And in June of 2015, I bought it for $19.99.
Now I'm looking at the trial version of SmartDown II (version 0.8.2). It has been completely rewritten in C#. It remains a very capable markdown editor. But many things have changed.
Key changesOn my Windows laptop, SmartDown II takes longer to load than the original - about three times longer. But that's not surprising for a beta.
Once it does load, the differences are immediately apparent: now three panes are displayed. On the left is a directory window. Load a folder, and "snippets" - file name, date, and the first three lines of text - show up. The center pane still has a sandwich menu on the top; the character count has been replaced with a word count. That's far more convenient for writing, although hovering still gives a few more statistics. There are two more controls on the bottom. On the lower left is a toggle to either reveal or hide the snippet pane. Moreover, the snippet panel can be adjusted by dragging its border - much as with a spreadsheet column. On the lower right, another toggle lets you access various functions (spellcheck, line number, word wrap, highlight, layout, template, and preview). Preview - the html conversion of markdown - can be turned off, shown as the constant third pane, or shown as a separate window. While displayed on the screen, however, you cannot resize it, or the center pane to the right.
What worksThe snippet pane not only allows a more convenient way to work with multiple files (although only one at a time), it also shows a navigation of the currently loaded file. That is, it shows the headers, and lets you jump around the file by clicking on them. The snippets pane works as a nice way to assemble things from smaller documents. However, I haven't yet found a way to drag them around within the pane. So snippets can be combined and rearranged within an editor pane, but not within the snippets or file pane.
When you highlight text, SDII now offers some pop-up one-click formatting guides (bold, italics, header, links, footnotes, etc.).
GlitchesOn occasion, I get a white cursor blob, a graphic glitch that hangs around on screen even when I move the cursor away. Pressing a Return after it tends to make it go away. [Follow-up: not a bug, a feature. This highlights two spaces.]
Sometimes, using the cursor to move up or down causes a line number to flash on the top right of the screen. That's useless and annoying.
Spellchecking: the red underlining starts immediately and only ends when you get to a punctuation mark. That's irritating, too: it means that most of the time you're typing, there's a red squiggle appearing and disappearing on screen - the opposite of distraction-free. So I turn it off. [Right now, you have to do this not through the preferences menu, but through the pop-up on the lower right corner of the main screen.]
The highlight paragraph mode, at least in the standard display, whites out and underlines everything else, although that may be because I was fiddling with foreground and background defaults. So that gets turned off, too.
Preferences are a little mysterious: you're not always changing what you think you're changing. But that could be just the learning curve. Meanwhile, it might be handy to have a "reset defaults."
On occasion, there's a lag in the preview display. Sometimes, when I add a new paragraph (especially as a list), the rightmost pane toggles to a huge font, then settles back down.
Moving through the editor pane doesn't move through the preview pane; they scroll separately. That's probably more a design feature than a glitch, but it seems to me to require excessive scrolling.