Aren't there already email solutions out there that treat email as a to-do list, divide it into discrete projects and so on? I believe there should be some, bas

Aren't there already email solutions out there that treat email as a to-do list, divide it into discrete projects and so on? I believe there should be some, based on Allen's GTD method, if nothing else. (https://en.wikipedia.org/wiki/Getting_Things_Done https://en.wikipedia.org/wiki/Getting_Things_Done)