This site hosts the Gnork project, intended to design an extensible programming language (actually extensible, not as in XML).
Gnork's design philosophy is based on the assumption that extensibility can be implemented efficiently and that it aids in building a general-purpose language that can be specialised to a wide range of problem domains.
An extensible language is built out of a core language, which can be extended both syntactically and semantically; these two different types of extensibility should be considered separately.
Rather than trying to keep the language as small as possible, it will be kept as simple as possible (there is a distinction); therefore, if it is simpler to put a language construct into the core language, we will do so.
The language should therefore be considered to consist of a core language and a standard library implementing a variety of useful constructs. While at this early stage of the language's design the language may experience significant changes, due to its being extensible obsolete constructs from the old language can be supported without fuss.