Focus by Meaningful Things Focus is a flexible productivity timer with built-in support for OmniFocus. Define your work in OmniFocus and use Focus to help you bring it to fruition.
Spark Mail A polished email client with a focus on email prioritization. Spark Mail also has innovative support for teams and integration with OmniFocus.
Airmail An email client that allows you to create OmniFocus actions that reference emails, manually or automatically using rules.
Fantastical An alternative to Apple's Calendar app that provides enhanced functionality, a natural language interface, and OmniFocus integration.
Drafts Quickly and conveniently and capture text and then send it to OmniFocus and other destinations through the use of flexible, customizable actions.