[http://www.gap-system.org/Packages/sgl.html SmallGroups] by E. A. O'Brien, B. Eick, and H. U. Besche Small Groups Library. All groups of order up to 2000 (except 1024) and some infinite series of groups characterised by the prime number decomposition of their orders.

[http://www.gap-system.org/Datalib/trans.html Transitive Permutation Groups] by A. Hulpke Transitive permutation groups of degree up to 30.

[http://www.gap-system.org/Datalib/prim.html Primitive Permutation Groups] by C. Roney-Dougal and many other people. All primitive permutation groups of degree <2500.

[http://www.gap-system.org/Datalib/tom.html Tables of Marks] by G. Pfeiffer and T. Merkwitz Tables of marks for many almost simple groups.