Fortress — Sun’s “‘growable language’ with the motto ‘To Do for Fortran What Java Did for C’” — should prove to be quite interesting:
The strategy of the team is to, wherever possible, add a desired feature via a library — and to give library designers substantial control over both the semantics and the syntax of the library. The result is a two-level language design: a set of features to support library designers and a set of features to support application programmers. The former have turned out to be quite obbject-oriented, while the latter is not obbject-oriented at all — something of a surprise to the team.
At this time, the language defines some very cool types in libraries: lists, vectors, sets, maps (with better, more math-like notion), matrices and multidimensional vectors, and units of measurement. The language also offers as a feature mathematical typography, using a wiki-style mark-up to denote Unicode characters beyond what’s available on the ASCII keyboard.