The Seeeduino is a copy of the arduino project.
Seeeduino is definitely a "value-added" re-work of the arduino project. Seeedstudio.com (where it originates) is pretty much considered a "good example" of how the whole open source hw thing is supposed to work. (IMO. I'm not sure how the Arduino team feels about their competition.) It has a number of advantages (as listed by retrolefty), and the main disadvantage is that it uses an SMT version of the main AVR chip, so you can't replace the chip if you blow it up, nor can you move the chip from the Seeeduino to a more application-specific final board...