TsFreddie
It uses 0.7 protocol rather than 0.6. ddnet server will yell at you to get a ddnet client. And you can't play some of the 0.6 only servers. And it is made by one guy so it might not be as stable as ddnet, also dummy may behave differently in some edge cases since the implementation might be different. (edited)
thanks for some clarification.
Basically, I made F-Client when there was no bridge servers between 0.6 and 0.7 and I loved 0.7 and based my server modification on it, so I wanted a 0.7 client with more or less minimalistic, but most relevant ddnet features. It misses opengl 3 tho :( xD