Triangle Centers Tools
In addition to showing the triangle centers, this sketch has tools to find them for any set of three points. So it's a toolbox, really. The sketch was also useful for creating activeprompt questions. See the blogpost for more info: http://bit.ly/1gQTPbU
Which center is which? (Some fool left them unlabeled.)
Which centers can occur outside the triangles? When does that happen?
When do which centers occur at the same point?