This article contributes to defining the design space of program repair. Repair approaches can be loosely characterized according to the main design philosophy, in particular “generate-and-validate” and synthesis-based approaches. Each of those repair approaches is a point in the design space of program repair. Our goal is to facilitate the design, development and evaluation of repair approaches by providing a framework that: a) contains components commonly present in most approaches, b) provides built-in implementations of existing repair approaches. This paper presents a Java framework named Astor that focuses on the design space of generate-and-validate repair approaches. The key novelty of Astor is to provide explicit extension points to explore the design space of program repair. Thanks to those extension points, researchers can both reuse existing program repair components and implement new ones. Astor includes 6 unique implementations of repair approaches in Java, including GenProg for Java called jGenProg. Researchers have already defined new approaches over Astor. The implementations of program repair approaches built already available in Astor are capable of repairing, in total, 98 real bugs from 5 large Java programs. Astor code is publicly available on Github: https://github.com/SpoonLabs/astor.