the successor to Palm OS with Web 2.0 technologies, open architecture, and multitasking capabilities. DangerOS  from  Danger, Inc.  (closed source, proprietary) DangerOS was a largely  Java -based operating system for the  Danger Hiptop  line of smartphones produced by  Danger Incorporated  from 2002 to 2010, also sold as the T-Mobile Sidekick. In