TeamRetro is one of my best examples of good software!
We successfully use TeamRetro to organize Sprint Retrospectives for distributed teams. The tool fits very well because it requires minimum learning effort and delivers the expected result. I have never heard negative feedback about this tool and rather see a constantly growing interest from the individuals and departments who encounter and try the tool in our organization. Also, the sign-on (if required) is a simple one-two clicks procedure...the "tool" does not dominate the conversation and does what it supposed to do.
Ilya Z. Agile Coach - G2.com