Google Inbox is a better UI, but goes too far the other way towards wasting too much space. It's also missing some key features, and is still not a desktop client.
Also, neither one of them supports showing emails from multiple gmail accounts in a single inbox (unless you just blindly forward emails from one to the other, which you can do, but I'd rather avoid).
I recognize I'm being very picky here; mostly what I just want is Dropbox's Mailbox app, but they killed that off long ago, much to my eternal disappointment.
Imagine you read emails in an unread folder, where read emails disappear. This basically would functionally mark them as read until a preset amount of time passes, then they show up as unread again. It's a bit like that, only in your inbox itself.
It's not actually a part of the email specifications, but some people seem to like it.
It doesn't require a third-party server. Nylas did do it that way, but Mailspring aren't. It's local.
I'm curious, such as what?