The ACTS Collection is a set of software tools that hlep programmers write high performance scientific codes for high-end computers. The tools were mostly developed at DOE labs and univerisities. They are primarily designed to run on distributed memory parallel computers. The tools fall into four broad categories: numerics, framework, execution support, and developer support. Brief introduction to representative software packages in each category will be given. It will be followed by in=depth discussion of selected software tools, including Hypre, a library for parallel iterative solvers of sparse linear systems, SuperLU, a library for the direct solution of sparse linear systems, and more.