{
 "apps" : {
   "AppName1" : {
      "label" : "App Name 1",
      "versions" : [
         {
            "app_version" : "1.0",
            "application" : "appname1"
         }
      ]
   },
   {
    "AppName2" : {
      "label" : "App Name 2",
      "versions" : [
         {
            "app_version" : "1.0",
            "application" : "appname2"
         }
       ]
      }
   }
}

[Serializable()]
public class AppsRoot
{
    public List<AppDetail> apps;
}

[Serializable()]
public class AppDetail{
    public string label;
    public List<AppVersions> versions;
}

fastJSON.JSON.ToObject<AppsRoot>(myjsonstring)

fastJSON.JSON.ToObject<AppDetail>(myjsonstring-part)