AmigaDE is the Amiga 'Digital Environment'. It is built on Tao Group's elate, which in turn is built on top of a Virtual Processor system allowing it to run natively on a wide range of CPUs or hosted under another OS. VP code is abstracted from the hardware: binaries are 'write once, run anywhere'. It is Amiga's bid for the digital convergence market space (hnngh). Amiga content (hnngh) on your PDA, toaster, whatever.
DE is completely separate from AmigaOS4, although the two are (were?) going to converge to form OS5.
@Akira: Demo of Codename: Hellsquad is in the Zone. It looks quite amusing.