I developed Centask [1] to integrate, in one view, everything I need to complete a project/task, (Gmail emails, files, links, notes etc.) organize it in any way I want, and declutter my task list by scheduling single and nested items to appear only when I need the
Since it is Gmail centric I can email myself links and notes from any app.
It can take Gmail Inbox emails into Centask Inbox so email is just one more task treated exactly the same as todo items and links etc.
Since most of the third party tools I use are online I use Centask bookmarklet to add links to tasks in other apps/sites to Centask Inbox.
What made it stick for me was to process my Gmail inbox within Centask so I must use it, thus my agenda may get longer when I am busy but never gets out-of-date.