@oggy: I'm fairly new here myself, and based on what I've seen since joining, the most recently active branch has been Lite-Nu/Arc-Nu. Anarki (the nex3 branch) hasn't been as active lately. Checkout https://sites.google.com/site/arclanguagewiki/ for more info on them.
The extent to which these extend Arc varies, so you should browse through their respective source codes as that will give you the clearest view on this front. You may find some of the extensions particularly useful, or not depending on your needs.
The authors of these branches would be in the best position to advise how suitable they are for production sites. HTH.
