Scared is a 3D shooter in the style of Wolfenstein 3D.
It was originally written as a Java applet in 1998.
An executable jar is available here: http://www.brackeen.com/scared/
The source is organized as a Gradle project. You can build it from an IDE or from the command line.
Assuming Git and JDK 7 or newer is installed, open a terminal and enter:
git clone https://github.com/brackeen/Scared.git
cd Scared
./gradlew build
An executable jar is created in the build/libs folder.