Lektor, a Python-based SSG that I've used in the past, actually had a self-contained Mac app for a while that was maybe 75% of the way toward that. (IIRC, the app didn't let you edit templates and most site-level configuration; the idea was more that you got things set up in a more programmer-nerd way first and then used the app for site maintenance/deployment.) Unfortunately, the app broke a few years back and nobody left developing Lektor seems motivated to fix it.
I've seen one other SSG that has an app, Publii, but I've never used it. My impression is that it wasn't as full-featured as Lektor, which could be made to do a lot of neat things. Although if Publii's app still works, that's one big thing Lektor doesn't have, so... :P