SquareOne is described as 'Email. Stress-free' and is an app in the Office & Productivity category. There are more than 10 alternatives to SquareOne for a variety of platforms, including iPhone, iPad, Android, Android Tablet and Mac. The best alternative is Microsoft Office Outlook. It's not free, so if you're looking for a free alternative, you could try Spark or myMail. Other great apps like SquareOne are TypeApp (Free Personal), Unibox (Paid), Polymail (Paid) and MailTamer (Paid).
TypeApp is an all-free, beautifully designed, universal email app, capable of managing unlimited number of mail accounts from various providers, allowing for smart push notifications while enabling personalization across multiple email accounts.
myMail is the smart email app for managing all your accounts on iOS and Android. Use myMail to manage messages in your Gmail, Hotmail, Live, Outlook, Yahoo, MSN, iCloud and AOL email accounts at once. The app also supports any IMAP and POP3-enabled mailbox.
Your inbox is already a task list - make it a great one. Taskbox allows you to manage your tasks and todos where they already are -- your inbox -- without forwarding or cutting and pasting them to another app.
EmailTray is a smart email client and an email notifier for POP3 and IMAP email accounts, including Gmail, Hotmail, Yahoo mail and AOL. EmailTray intelligently ranks messages, prioritizes them into 4 Inboxes and alerts you only to the most important.