@Dimitrios: Yes, it is an American Purple Gallinule (or a "purple swamp hen").

From a description of it, "This medium-sized rail is unmistakable, with its huge yellow feet, purple-blue plumage with a green back, and red and yellow bill. It has a pale blue forehead shield and white undertail."

@Martin: I took it at Brazos Bend. I don't think they are super common - mostly you see the black moorhen version.