Line by line parsers are much much more limited. This can support syntax transformations and html attributes. This is more of an html-alternative in terms of capability. Markdown links are ugly and you need double space instead of single space for every space you input. I could do something like replace things nested in as italics but I'd rather have normal characters not turned into formatting. Lisp might look ugly in comparison to python, but not html and bbcode.
I'm not sure what you mean about double-spacing either. Line breaks (<br />) are made by adding two spaces to the end of a line. If you don't like that, try GitHub-flavored Markdown [2].
I was only aware of the last one. This has the capability to be used as a replacement to html, not just a limited subset. It can also do syntax transformations like the table, which also accepts other syntax transforms and tags. Markdown can't take html attributes either.
