What are some alternatives?
When comparing PopTrayU and POP Peeper, you can also consider the following products
nPOPuk - nPOPuk is an ultra-small, but comprehensive, e-mail client that runs on a wide range of...
Mia for Gmail - A desktop email client for your Mac, without a browser !
Gmail Notifier Pro - Gmail Notifier Pro is a Gmail notifier for Windows that can check multiple Gmail accounts for new mail and display notifications. Also supports Google Calendar, Google Reader & Google News.
Kiwi for Gmail - Dedicated Gmail client with clean integration of Google Calendar, Contacts, Google Drive, and...
Google Mail Checker - Displays the number of unread messages in your Google Mail inbox.
Wavebox - Bringing the Gmail & Google Inbox experience to your desktop in a neatly packaged app