Chrome: Streak is a new web service and Chrome extension that adds a ton of useful features to your Gmail account, including the ability to compose messages and schedule them to be sent at a later date, text expansion that works by menu or keyboard command, and the ability to manage your personal projects.
Streak was built as a CRM-tool for business types who want to track their sales and leads, but the service has strong personal appeal as well. The "send later" feature integrates completely with Gmail, and your composed message lives in the Drafts folder until its scheduled time, when it'll be sent without you having to be logged in to Gmail to see it go. The "snippets" feature is essentially Gmail-only text expansion, and it works just like canned messages -- you can create expanded text and save it, and then toggle it from the menu, or by pressing a keyboard command you can specify when you configure the snippet.
Beyond the basics, Streak also allows you to create "pipelines", or different types of projects you want to use Streak to manage. The company has tutorials where people use the service for everything from bug tracking to fundraising to event planning. Inside each pipeline is a "box", or an individual to-do or sub-project. You can kick off a box by selecting a message or conversation from your inbox, giving it a name, and the box will be created with all of the necessary people added to the contacts for that box. This way you can keep track of who's involved in your project and what they're doing. Adding new to-dos and assigning them to the right part of your project is as simple as clicking "new box" and typing in the details. When you've added all of your to-dos, you can group or filter them based on tags, the stage of your project they're in, who's responsible for them, and more.
Streak is completely free to use, and it does require access to your Google account in order to work. You don't give Streak your password -- you grant it access via OpenID, and the service's privacy FAQ makes it clear what they can and can't see. If you're looking for a to-do manager or project tool that's more robust than Google Tasks but still integrates with Gmail like a dream, Streak is seriously worth a look.