HEY - Email at its best, new from Basecamp.
SubscriptionZero - Declutter your Inbox by combining your newsletters emails
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
GoodByEmail - Declutter your inbox without giving third-party access to your emails! Reclaim GBs of storage, unsubscribe from pesky emails—all while keeping your emails off our servers. Experience full privacy with GoodByEmail, even offline!
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
The Email Game - Get to inbox zero with game mechanics