Inbox was announced by Gmail and Google late last year. While it's still invite-only, it was only available for those with a Gmail account. So those with an apps account for work or for school could not use it. However, that's about to change. According to Google's Sundar Pichai, who's in charge of apps, Android and Chrome, stated that Inbox for Gmail will be rolling out to Google Apps users "Imminently".
Yesterday, we informed everyone that Inbox was rolling out to other browsers like Safari and Firefox (still no support for Internet Explorer). As well as coming to Android Tablets and the iPad. Which means more people will be using Inbox by Gmail now. Sundar also updated that to say that it'll be coming to Google Apps users soon as well. Which means even more users. I tried using Inbox from my own Google Apps account, but it appears that it's not rolled out to me just yet. We'll have to keep an eye on that.
You will likely still need an invite to use Inbox by Gmail if you are an apps user. Which you can get a hold of one by emailing [email protected] for an invite. You might get one instantly, it might take a bit. There's also another way to get an invite and that's to ask one of your friends that already has Inbox, as they will have some invites as well. You'll probably want to ask them nicely though, if you really want the invite.
Google still expects Inbox to replace Gmail, although not in the immediate future. Probably in a few years. I'm expecting Inbox to be in beta or invite-only form for quite a while since Gmail was actually in beta for almost 7 years.
If you're a Google Apps user and have gotten an invite, just sit tight with that invite, you should be able to use it real soon. If you've gotten Inbox rolled out to your Google Apps account, be sure to let us know in the comments down below.