This paper motivates how collaborative tools are needed to support modern computational science, using the case study of a distributed team of numerical relativists developing and running codes to model black holes and other astrophysical objects. We describe a summary of previous tools developed within the collaboration, and how they are integrated and used with their simulation codes which are built using the Cactus framework. We also describe new Cactus tools which use the Twitter and Flickr services. These tools are fundamentally integrated with the code base as Cactus modules and provide reliable, real-time information about simulations that can be easily shared across a collaboration.

Nomadic Migration describes a technology, which provides an application with the ability to seek out and exploit remote computing resources by migrating tasks from site to site, dynamically adapting the application to a changing Grid environment. By automating the detection and usage of free resources in a global Grid, we achieve a significantly faster throughput than by manually interfacing with these resources. In this Paper we discuss the Peer-To-Peer strategy as an approach to provide a fault tolerant service infrastructure, required for a stable Grid Migration Service in an intrinsically disruptive Grid environment. The migration technology presented here is e.g. used with large-scale, Cactus based HPC simulations.

We present a synopsis of the Grid Application Toolkit, under development in the EU GridLab project, along with some of the new application scenarios which it will enable.

The Testbed and Applications working group of the European Grid Forum (EGrid) is actively building and experimenting with a grid infrastructure connecting several research-based supercomputing sites located in Europe. The paper reports on our first feasibility study: running a self-migrating version of the Cactus simulation code across the European grid testbed, including "live" remote data visualization and steering from different demonstration booths at Supercomputing 2000, in Dallas, TX. We report on the problems that had to be resolved for this endeavour and identify open research challenges for building production-grade grid environments.

We describe the design and implementation of a technology which provides an application with the ability to seek out and exploit remote computing resources by migrating tasks from site to site, dynamically adapting the application to a changing Grid environment. The motivation for this migration framework, dubbed "The Worm", originated from the experience of having an abundance of computing time for simulations, which is distributed over multiple sites and split in time chunks by queuing systems. We describe the architecture of the Worm, describing how new or more suitable resources are located, and how the payload simulation is migrated to these resources following a trigger event. The migration technology presented here is designed to be used for any application, including large-scale HPC simulations.

Cactus is an open source problem solving environment designed for scientists and engineers. Its modular structure facilitates parallel computation across different architectures and collaborative code development between different groups. The Cactus Code originated in the academic research community, where it has been developed and used over many years by a large international collaboration of physicists and computational scientists. We discuss how the intensive computing requirements of physics applications now using the Cactus Code encourage the use of distributed and metacomputing, describe the development and experiments which have already been performed with Cactus, and detail how its design makes it an ideal application test-bed for Grid computing.