Apache Ant - Automation build tool, similar to make, a library and command-line tool whose mission is to drive processes described in build files as targets and extension points dependent upon each other. (Source Code) Apache-2.0Java
Apache Maven - Build automation tool mainly for Java. A software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information. (Source Code) Apache-2.0Java
Bazel - A fast, scalable, multi-language and extensible build system. Used by Google. (Source Code) Apache-2.0Java
Bolt - You can use Bolt to run one-off tasks, scripts to automate the provisioning and management of some nodes, you can use Bolt to move a step beyond scripts, and make them shareable. (Source Code) Apache-2.0Ruby
GNU Make - The most popular automation build tool for many purposes, make is a tool which controls the generation of executables and other non-source files of a program from the program's source files. (Source Code) GPL-3.0C
Gradle - Another build automation system. (Source Code) Apache-2.0Groovy/Java
Rake - Build automation tool similar to Make, written in and extensible in Ruby. (Source Code) MITRuby