Distributed computing over large networks often suffers poor performances due to architecture heterogeneity and synchronization delays. This is the case of classical computing libraries which are dedicated to parallel machines or clusters. To achieve a better efficiency on multi-sites heterogeneous networks, one can use asynchronous algorithms which are less sensible to communication delays and loss of messages. Implementing such algorithms with classical MPI versions is not the best choice. We propose Jace, a Java environment dedicated to distributed asynchronous computations, and more especially to asynchronous iterations-asynchronous communications algorithms. It contains all facilities to build a parallel virtual machine and to implement computing tasks in a message passing style. Communications have a special semantic adapted to asynchronism. First tests on a simple Jacobi algorithm clearly show the benefits of our environment to compute on a multi-site heterogeneous network, that is, the Grid.