This paper presents the design and implementation of the GARF system, an object-oriented platform that helps programming fault-tolerant distributed applications in a modular way. The originality of GARF is to separate a distributed object into several objects, the complexity of distribution and fault-tolerance being encapsulated in reusable classes. The use of those classes by the GARF system is based on a run-time mechanism of invocation redirection, where most other systems use inheritance, a compile-time mechanism. Our runtime, which supports the GARF object model, is written in Smalltalk. It is presented in detail, as well as the reusable classes that support fault-tolerance. Fault-tolerant objects are implemented using groups of replicated objects. Our Dependable Object Toolkit provides group management facilities at the object level. Object groups are built on top of the Isis toolkit, which provides group management facilities at the Unix process level. Our mapping of object groups on process groups and our interfacing of Smalltalk and Isis are detailed. Performance analysis and a first evaluation of our prototype are also presented.