The Textual Modeling Framework (TMF) is an umbrella project under the Eclipse Modeling Project (EMP). It hosts two different framework for implementation of textual syntax for EMF models (aka Ecore models).
TCS (Textual Concrete Syntax) comes from GMT. With TCS one annotates concrete syntax information to existing ecore models. The editor is not generated but interpreted.
Xtext is a part of the openArchitectureWare framework, but is now developed under modeling.tmf.xtext. It still will be a part of future openArchitectureWare releases. With Xtext one can also write grammars for existing meta models. In addition it is possible to derive ecore models from grammars, since a grammar contains sufficient information about the structure of parsed models. Xtext implements EMF's resource API (it is possible to use xtext based syntax transparently through the resource load and save functionality, hence you can use e.g. GMF editors for Xtext based DSLs). Xtext also generates a rich IDE for your language, which can be easily customized via dependency injection.
It is intended that at some point there will be only one framework instead of two. Requirements and thoughts can be discussed here