Clone the NetBeans Incubator sources to your machine:
git clone https://github.com/apache/incubator-netbeans
Build using JDK 8 and Ant 1.9.9 by traversing into the cloned incubator-netbeans directory and invoking the ant build:
Once the build is complete, traverse into the nbbuild/netbeans directory to see the resulting IDE build. Run the IDE by invoking the executable or shell script contained within nbbuild/netbeans/bin.