It is difficult to describe GROK, but it is a compiler toolchain at a high level. As polygot programmers, we have used different IDEs and editors for different languages, but there is no one text editor or IDE to rule-them-all -- simply because each language has its own idiocracies and what not. Grok tries to solve the toolchain parity problem:
My project is accomplishing this lofty and almost insanely ambitious goal through the (A) normative, language-neutral, cross-language definitions of, and (B) subsequent standardization of, several distinct parts of the toolchain: (I) compiler and interpreter Intermediate Representations and metadata, (II) editor-client-to-server protocols, (III) source code indexing, analysis and query languages, and (IV) fine-grained dependency specifications at the level of build systems, source files, and code symbols.
In other news, the .NET foundation open sources significant part of the .NET platform, including the .NET compiler platform (Roslyn). (However, language differences are still tricky -- Roslyn provides two distinct compiler APIs for C# and VB.) Microsoft also released CTP3 (Community Technical Preview) of RyuJIT (a .NET JIT compiler).