Can a Unity project be open-sourced?

Okay, question two: Can a Unity (Free or Pro) project be licensed as Open Source software?

There's no reason not to open source a project you wrote, and there are several already, including UnitySteer (MIT license) and Path (GPL).

The main considerations would be ones that apply to your code regardless of Unity, including if you own it, and the terms of any code you link to (for instance, if you code depends on GPL'd, you must distribute it as GPL too).

As long as you purchased all the necessary tools legally, I don't think that this has anything to do with Unity.

There is also the issue of redistributing the source code of the standard assets... the copyright might get messy if you changed the code.

Do you know what licence the standard assets are?