Dinosaur eels are aka Asian or African Rope fish. They should have a place to climb out of the tank since they do spend part of their time breathing air. I do not know if they are true freshwater or brackish water, but I've kept them in freshwater without any problems. They're peaceful predators, eating things that they can ambush and engulf. They are also prone to a worm parasite on their scales that is difficult to get rid of, but don't seem to harm the fish unless they get really over-populated.
Dragon eels are sand shifters, and need to be on a very fine sandy substrate in order to eat. I don't know if they are true freshwater or brackish water, but I've kept them in true freshwater without any problems.
I do not know if Peacock or Tiretrack eels are true freshwater or brackish water. I've kept them in true freshwater without any problems. They also like to bury in a fine gravel/sand substrate.
Morays (snowflake, cloud, green, wolf etc) are definately marine salt water, although I've seen them for sale for brackish and fresh water, I've never kept them in anything but marine salinities.
~~Colesea