Shift Is a Desktop Email Client That Easily Switches Between Gmail Accounts
Windows / Mac / Linux: If you use multiple Gmail accounts, you’re used to having multiple tabs for everything. Shift solves this problem by opening multiple accounts in one convenient desktop client.
Shift gives you separate tabs to access Gmail, Calendar, and Google Drive in one window. If you want to switch to a different account, just click the profile tab on the left side of the window. Shift is free for two accounts. If you need more, that’s $ 20 per year for unlimited accounts, which also includes support for Outlook.com accounts.