I know Dereos and its regulars pretty well; I meet many of them at least weekly.
The sims in Dereos run on various different OpenSim versions. It still largely depends on Arriba because it still largely depends on specific modifications added in Arriba.
OpenSim Arriba FreAki, as used by the grid server and various region servers, is a fork of ArribaSim, an older fork of OpenSim from, I think, before 0.8.2.1. IIRC, it was Freaky Tech, a Dereos resident, who created Arriba. FreAki is now maintained by Akira Sonoda. But a whole lot of new additions from over six years had to be ported over from vanilla manually, including BoM and viewer AO. I'm not sure if the current version is 1.3.6 or 1.3.7. The latest version was made after feedback from me, particularly regarding BoM, but IIRC, Dereos uses two versions. It is no longer maintained.
OpenSim Aki DotnetArriba, which is only used by region servers, is basically a fork of vanilla OpenSim, but Akira has added a few things from Arriba for it to be compatible to the grid server. It behaves much more like vanilla. I'm not sure if this is still maintained, for Akira has something new in the making.
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