Basecamp is a project management solution that provides a secure space online where people working together can organize and discuss everything they need to get a project done. See it, track it, discuss it, act on it. Tasks, discussions, deadlines, and files - everything’s predictably organized in Basecamp.
Every time a new project or initiative comes up, spin up a new Basecamp in your account, name it ("Q3 Marketing Pitches", for example), invite the people involved, and keep everything related to that project neatly organized inside that Basecamp.
Now everyone knows where everything is, they know what they need to do, and nothing slips through the cracks. Basecamp even works over email -- people who prefer email can simply reply to discussions via any email app without ever having to log into Basecamp.
Note: Your first Basecamp is free. The pricing schema can be found here.