Omega was developed as an extension of TeX, to use with multilingual texts, expressed in a variety of input encodings. Omega uses 16-bit, Unicode-encoded, characters. It provides many innovative concepts, notably including the “translation process” that takes a character stream and transforms it according to various processes that may be internally specified, or be a separate program.
While Omega showed a lot of promise at its mid-1990s announcement, progress was slow, and development was essentially dead by the time that one of the original developers withdrew (taking with him a bunch of research students).
Before that distressing event, a separate thread of development had started, to produce a program called Aleph, which merged the facilities of e-TeX into a stable Omega codebase and added other extensions. Aleph also proved an attractive platform for many people; but its development, too, has dried up.
A presentation at EuroTeX 2006 claimed that development of Omega was picking up again, in parallel with research into what the (new) developers consider a rational scheme for supporting TeX-style typesetting. The new system was to be known as Omega-2 (Omega subscript 2), and was to be designed in a modular fashion so that support of new facilities (such as use of advanced OpenType fonts) could be added in a relatively straightforward fashion. A quick web search leads to a recommendation that potential users consider LuaTeX instead; fortunately, lessons learned in Aleph project have been carried forward in the development of LuaTeX.