Photos.app is really the best option. You can also checkout Lyn, but it doesn't have a direct Gmail option: https://www.lynapp.com/
One round about solution might be to get MailPlane, a "wrapper" for Gmail that would add an entry to the share menu, see: http://mailplaneapp.com/help/send_via_mailplane_3_share_extension.html
Yeah, I tried SparrowMail, but I can't see any benefit for me really and I'm so used to the Gmail interface. I can't think of a time when I've need my mail offline or haven't had a web connection of some sort. Google's search is faster and I use MailPlane and get Growl notifications. Also I use an SSD, so space is at a bit of a premium and Sparrow used up a lot, weirdly more than the space Google tells me the total of my email is. I guess it just depends on what type of interface you prefer.
If you like GMail's web interface and still prefer a desktop app with Growl and all, then I highly recommend MailPlane. You also get a discount for educational institutions.
I used MailPlane for a while. It is "just" a wrapper around the gmail web interface but it makes it behave like a proper Mac app. It's got a free trial, check it out. http://mailplaneapp.com
When I was in my heaviest gmail usage days (4 accounts, getting a lot of mail all day) it was a godsend.
The only reason I don't use it these days is most of my email comes from work and they don't use gmail.
If your email is primarily gmail, I would recommend Mailplane. I've been using it since the beta, and I love it. It's stable and easy to get at messages offline. But I funnel all of my email through my gmail account. http://mailplaneapp.com/
When I still had Google Mail, I used Mailplane. It's basically a wrapper around the Google Mail/Inbox web interfaces that provides more integration with macOS (notifications, native previews, integration with other Mac apps).
iOS: Outlook
Mac: Right now I'm testing Mailplane, which I'm really liking so far. App designed specifically to handle Gmail accounts. Normally I use the browser.
My gripe with the browser though is that I have a personal Gmail account and a work Gmail account, so I pretty much have to have personal in Safari and work in Chrome so that my emails and Drive documents don't get confused. Being able to separate them out in to a separate mail app, so I can just use Safari, is kind of nice.
It's not free, but MailPlane does this. It's essentially a wrapper around the Gmail website, but has a menubar item and supports multiple Gmail accounts. Here's a screenshot of mine.
I mean, Mailplane comes to mind. But by "Tabs" you just mean different inboxes. Just make folders with rules if that concept is what's interesting, otherwise you're stuck with the web interface or something like Mailplane. Or even make a Fluid instance just for Gmail if you just don't want web browser chrome in the way.
Puts me in mind of Mailplane, actually. For that purpose (desktop app wrapper for Mac OS X), it's not a terrible implementation (i.e. it enables Gmail to catch "compose mail" events better than the hack that opens the browser), but it still feels half-assed.