Boo
boo is a new object oriented statically typed programming language for the CLI (common language infrastructure) with a python inspired syntax and a special focus on language and compiler extensibility.

Coco/R
Coco/R is a compiler generator, which takes an attributed grammar of a source language and generates a scanner and a parser for this language. The scanner works as a deterministic finite automaton. The parser uses recursive descent. LL(1) conflicts can be resolved by a multi-symbol lookahead or by semantic checks. Thus the class of accepted grammars is LL(k) for an arbitrary k.

IronPython
Implementation of the Python language targeting the .NET and Mono platforms.

Nemerle
Nemerle is a high level typed programming language for the .NET platform. It offers functional, object-oriented and imperative features. It has a simple C#-like syntax and a powerful meta-programming system. Features that come from the functional land are variants, pattern matching and type inference.

P#
P# is a compiler which facilitates interoperation between a concurrent superset of the Prolog programming language and C#. This enables Prolog to be used as a native implementation language for Microsoft's .NET platform. P# compiles a linear logic extension of Prolog to C# source code.