Arcee is a transformer lady or gynoid. Arr is a pirate's most beloved throaty grunt. RC also stands for rollercoaster and, in this case, for RELEASE CANDIDATE.
AGS 3.3.0 is now at the RC stage where things may get polished and fixed a bit more but, and this is important, where stuff can be considered feature complete. Old dogs like me may stick to 3.2.1 for a while, or in Ponch's case to 1.2, but really, I can't stress this enough- AGS has been made open-source, and many hands have shaped this new version, and it looks nice indeed.
See for yourself, though! That blue line up there is a link.