Pyrus is a webapp that makes it easy to organise multiple projects at the same time, bring in others and have them collaborate with you, manage due dates and set deadlines, all from the same window. Think of it like Gmail for project management, with a dash of Google Wave for good measure.
If you don't remember the now-defunct Google Wave, the service made it easy to collaborate with others on constantly-living documents and workspaces. Pyrus is a bit of a cross between that and Gmail -- in fact, its interface borrows heavily from Gmail's design cues (which makes it simpler to learn if you're familiar with Gmail). Pyrus makes it easy to add new tasks or projects, jump across projects to something you need to work on, see what's happening just today, or what all of your next actions are across everything you're working on.
Similarly, if you work in an organisation, you can use Pyrus to collaborate with others, get their comments and updates on your tasks, farm out responsibilities, and share items. If you prefer, you can use it as a basic to-do webapp, but its real power comes from the fact that it makes managing multiple projects easy in a simple, easy-to-use interface. The service also supports Android Wear, so if you have a smart watch, you can use Pyrus along with it.
Pyrus is free(mium), with premium plans offering extra features, but the free plan should be enough for most people. Hit the link below to try it out.