Nikolaus is just his internal testing, the one from me is an outdated aTc one (as we need to find a way to make the buildserver reliable), so aTcs one is the recommended one.
Well, it is not only for "internal testing", but "external" for Goldelico users and is a continued effort. GDC simply runs a multi-architecture GNU/Linux distribution project where SD card images can run (almost binary compatible as long as technically feasible) on the GTA04, the Letux variants, the BeagleBoard, BeagleBone, OMAP5432EVM, OpenPandora, Neo900, Pyra, and more to come.
It combines a patched upstream kernel with some Debian LXDE/XFCE4, or Android/Relicant, or QtMoko or QuantumSTEP as handheld device "Desktops" or "Palmtops".
This all will be extended in the next months (maybe with a rename to remove the thigh connection with the "GTA04" device the current project name seems to imply).
Therefore it is not (and does not try to be) "the" Pyra OS. It is just one option that can also be installed. It is optimized for multi-platform support. With that it helps us during development of the Pyra hardware for two things:
* hardware bring-up needs an OS that we can easily modify and extend to support new chips and test situations, but is also mature enough so that we don't have to fix bugs in other areas than the hardware-kernel interface
* upstreaming of kernel patches (since the kernel is also multi-platform) - to test them you also need some OS to do tests
ED has an almost orthogonal goal: make "the best" OS for the Pyra. Therefore he provides an optimized image for the Pyra, optimized for gaming, emulators, speed, etc. But it runs only on the Pyra and no other device.
So the gta04-rootfs, gta04-makesd, gta04-kernel projects etc. do not intend to replace the Pyra OS or even compete. It is just something that can be the better choice for some users and is for us during the current project phase.
And, this multitude of choices allows to run different binaries on the device and this sometimes reveals issues we would to have seen.