Google has rolled out Inbox by Gmail to iPad and iPhone users, as well as those with the Firefox and Safari web browsers.
The app was firstly available in the German App Store, but has now rolled out in more countries, and - as a beta - remains invite-only.
Taylor Kourim, software engineer at Google, said on the Gmail blog: "It's always hard to know when it's time to share a new product, because there's always just a few more things you want to do. Today we're happy to check off some of these to-dos for Inbox, making it easier to use on more devices and browsers."
Inbox by Gmail was launched last year and turns the email inbox into a 'to-do' list, helping users act on the things required in an email.
That action could be to reply, set up a meeting or pay or bill or book a flight, for example.
When users read an email, it doesn't just disappear into the 'read' pile, but can be filed into 'pinned', 'snoozed' or 'done'.
Pinned puts it in a prominent place - the equivalent as 'starred' in the standard Gmail app.
Snooze will put the email on the backburner until users are ready to deal with it, sending a reminder at a pre-determined time, while Done means any task associated with that email have been completed.
"Done" emails won't be removed from the inbox, but will sit in the background so they don't get in the way of Pinned or Snoozed emails.
The application also groups together similar apps, like promotions, purchases, travel and anything else users want in the same inbox. Each email has a handy preview too, so users can find the right one without trawling through all their emails - or even opening them.
The Inbox by Gmail app was first launched on Chrome and Android tablets.
