Does anybody have some info about its state?
It's had some things updated in 2013, so I believe someone is still running it. I tried to find out who via their mailing lists, but the lack of a new live CD is discouraging. The live CD installs at least, but can't be upgraded properly.
Is it a live project?
It seems not to be anymore.
Is it safe to use it?
I would only virtualize it; you can easily break it if you try to upgrade glibc. I had problems with RootLess, so I'd personally use VirtualBox (VMDK, dynamic allocation) for it. It installs, but you can't upgrade the core applications (glibc and so on). I'm looking into workarounds now.
Is there any other distro that uses a similar file structure?
None that I know of. The core idea is concurrent applications versions I think. Despite the file structure is appealing.
PS.: anyone, feel free to edit/fix this post, I want to know better what is going on too..