+1 for the Taskpaper app recommendation. If you're happy with Taskpaper mode in Editorial and looking for something to work with the same files on your Mac, it's a no-brainer.
That said, one of the (many) reasons I love Editorial is that it allows you to build your own solutions. You can implement your own basic support for simple Github style tasks in a workflow with three action steps:
1: extend selection (select the entire line)
2: find "[ ]" and replace with "[x]"
3: replace selected text (with input)
Assign an approriate shortcut, then run this on any Github style task you want to mark done. You could, in theory, use this kind of thing to manage your tasks in a way that respects both conventions. Say, prefix your tasks with "- [ ]", then configure your "mark done" workflow to add both a "[x]" and a "@done" tag, though that would actually mean a little more work at the Mac end for comparable functionality.
Point is, even if the functionality you want isn't already baked in, with a little DIY, Editorial's a beautifully extensible app that allows for a lot of flexibility in setting things up in a way that makes sense for you.
