Those casinos including English Harbour used to be on Microgaming software but the owners developed their own casino software to use. Over the years, OddsOn eventually changed its name to Vegas Technology.
The software company nearly went out of business after the 2011 Black Friday when many poker domains were seized, the casino group decided to shut down and call it quits, this included the sites that took players and the casino software. The casinos remain closed to date but the software has been picked up by a new group and is currently known as Wager Gaming Technology.
This software will always have a fan base as some of the games have been online for a good 15 years. Now only a few casinos use this software and those casinos mainly take US players.