Why does it look almost identical to Slack
Don't you know? It's just the natural evolution of software -- eventually every UI converges until it becomes Slack. Slack is sort of like the Macbook Air of software. Ask HP why all their laptops look like an Air, and it's just the "natural evolution of the form". (cf. Samsung / iPhone)
Ghost has sorta looked like that since it's launch in 2013. And the "slack" look seems to have been around since the early Metro apps for Windows 8 (see MetroTwit 2012)
Great question! The answer has to do with design patterns. Looking at the vast majority of websites out there, they all follow a similar format... Header, content, sidebar, footer, etc. Some are more unique, and lay that information out in a different way (or omit portions), but it can usually all seem to fall into established patterns. Desktop software UI's are no different either.
It's not that major players in the tech industry have lazy designers on staff, it's that there are established patterns designers know their users are familiar with. Reinventing the wheel can produce something amazing... But more often than not you just end up with a wheel requiring an instruction manual while your competitor's wheel is more user friendly. Design is a constant question of what may be too innovative, and what still seems approachable to the user.
is this satire?
LOL c'mon look at the selected left-col indicators. Don't BS this blatant-af copy.
Twitter, Airmail, and a few dozen other mac clients have used that navigation pattern. It's not copy and paste, it's good design. The side navigation follows a hierarchy into the sidebar, which leads into the content pane(s). It allows you to see a lot of information in an overview without being too crowded.
Twitter is descended directly from Tweetie. Sparrow copied Tweetie. Airmail copied Sparrow once development was discontinued. None of them used the left-aligned partial roundrect selected indicator.
John O'Nolan has a track record for shamelessly 'borrowing' interface design aesthetics. I remember when his blog copied DigitalMash, and now this looks like Slack. It's not a big deal- everyone's copying everyone these days, but as a CEO and 'head of design' it doesn't suggest beneath the surface there's anything earth shattering going on.
People get distracted blogging in a browser window?
For me (not a Ghost user), the advantage would just be in having a dedicated dock icon for multitasking. Sort of why I use Epichrome for certain webapps (twitter/netflix mostly)