Boot up either standalone or the domain and take a look at boot.log. There will be a stacktrace similar to:
13:10:53,891 TRACE [org.jboss.modules] Failed to define class org.jboss.as.ejb3.EJB3Extension in Module "org.jboss.as.ejb3:main" from local module loader @7d2452e8 (roots: /home/carlo/work/jboss-as/build/target/jboss-7.0.0.Alpha2/modules): java.lang.LinkageError: Failed to link org/jboss/as/ejb3/EJB3Extension (Module "org.jboss.as.ejb3:main" from local module loader @7d2452e8 (roots: /home/carlo/work/jboss-as/build/target/jboss-7.0.0.Alpha2/modules))
at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:374) [:1.0.0.Beta13]
at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:250) [:1.0.0.Beta13]
at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:70) [:1.0.0.Beta13]
at org.jboss.modules.Module.loadModuleClass(Module.java:486) [:1.0.0.Beta13]
at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:178) [:1.0.0.Beta13]
at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:270) [:1.0.0.Beta13]
at org.jboss.modules.ConcurrentClassLoader.access$400(ConcurrentClassLoader.java:42) [:1.0.0.Beta13]
at org.jboss.modules.ConcurrentClassLoader$LoaderThread.run(ConcurrentClassLoader.java:339) [:1.0.0.Beta13]
Caused by: java.lang.NoClassDefFoundError: org/jboss/as/server/Extension
at java.lang.ClassLoader.defineClass1(Native Method) [:1.6.0_22]
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) [:1.6.0_22]
at java.lang.ClassLoader.defineClass(ClassLoader.java:616) [:1.6.0_22]
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) [:1.6.0_22]
at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:370) [:1.0.0.Beta13]
... 7 more
Caused by: java.lang.ClassNotFoundException: org.jboss.as.server.Extension from [Module "org.jboss.as.ejb3:main" from local module loader @7d2452e8 (roots: /home/carlo/work/jboss-as/build/target/jboss-7.0.0.Alpha2/modules)]
at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:186) [:1.0.0.Beta13]
at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:270) [:1.0.0.Beta13]
at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:52) [:1.0.0.Beta13]
... 12 more
Clearly this shows that org.jboss.as.server is the missing dependency.