Attempto Controlled English (ACE) - a specification and knowledge representation language - is a controlled subset of standard English that allows users to express technical texts precisely, and in the terms of their respective application domain. ACE texts are computer- processable and can be unambiguously translated into first-order logic. ACE appears perfectly natural, but - being a controlled subset of English - is in fact a formal language with the semantics of the underlying first-order logic representation. ACE, and its tools (e.g. Attempto Parser, Attempto Reasoner), are intended for domain specialists who want to use formal notations and formal methods, but may not be familiar with them. Thus the Attempto system has been designed in a way that allows users to work solely on the level of ACE without having to take recourse to its internal logic representation. ACE must be learned, but this amounts to learning the differences between ACE and full English, formulated as a small set of ACE construction and interpretation rules.
ACE has been used to specify a number of smaller problems and to provide natural language interfaces to formal systems. Furthermore, ACE has been adopted as the controlled language of the EU Network of Excellence REWERSE (Reasoning on the Web with Semantics and Rules).
More information on ACE: http://www.ifi.unizh.ch/attempto.