DUDE can be used to extract data from database instances that cannot be started and that are effectively scrap. It can also be used as a fast method to extract data. I would not recommend this for production though as you are unlikely to be supported. As a crash recovery tool though it is a lifeline to some people.
Kurt has now started a site called ORA-600 to promote DUDE as jDUL is now known. There is a good introduction to DUDE on the front page of the site that includes a list of all of the features supported. It works with Oracle 8,8i,9i and 10g, the dictionary can be recreated, missing SYSTEM tablespaces can be dealt with, most data types are covered, whole tablespaces can be recovered, pl/sql, most major platforms are supported, chained, migrated rows, trailing NULL's and partitioned tables are supported. Version 2.0 will include IOT's LOBS and RAW's soon.
If you have a dig around Kurt's site, you will find a nice description of the tool, a history page and also details of the services offered. Miracle AS, Mogens company are the preferred resellers to contact if you need to hire this tool.
Kurt has also includes a nice paper DUDE 2.0 primer that details how DUDE can be used to extract data from your Oracle database.
It is possible to get a demo version from Kurt, follow the links on his site and use Kurt's security protections. You need to fill in a config file and run DUDE_PROBE.jar against your database and then it is possible to get a demo that will dump just two tablespaces DUDE and SYSTEM.
I have updated my Oracle Internals page to add details of Kurt's paper and I have also added an Internals section to my Oracle Security Tools page to include this tool.