vxargs provides parallel versions of any arbitrary command, including ssh, rsync, scp, wget, and curl. One reason to use it is to control a large set of machines in a wide-area network or a big cluster. The main features are parallelism (for running many jobs at the same time), flexibility, visualization (users can monitor the total and per-job progress in a curses-based UI), and redirection, in which stdout and stderr of each individual job are redirected to files for further analysis.
w3af (Web Application Attack and Audit Framework) is a framework for finding and exploiting Web application vulnerabilities. It is easy to use and extend. The project has more than 125 plugins which check for SQL injection, cross site scripting (XSS), remote file inclusion, and more.
Waf is a Python-based framework for configuring, compiling, and installing applications to replace the whole GNU autotool chain (automake, autoconf, aclocal, autoheader, libtool, and make). It is extremely small (72kb), easy to redistribute (no installation required), and features several tools for building C, C++, Java, Gnome, C#, Qt4, or OCaml applications.