&RCWA; is a package for &GAP; 4. It introduces a new class of groups which are accessible to computational methods. In principle, this package can deal at least with the following types of groups and their subgroups:

Finite groups, and certain divisible torsion groups which they embed into. Free groups of finite rank. Free products of finitely many finite groups, thus in particular the modular group PSL(2,\Z). Direct products of the above groups. Wreath products of the above groups with finite groups and with (\Z,+).

With substancial help of this package, the author has found a countable simple group which is generated by involutions interchanging residue classes of the integers and into which all the above groups embed. This simple group has an uncountable series of simple subgroups, which is parametrized by the sets of odd primes.