What is ABBA World? It is an exhibit in the UK, an audio-guided tour through 25 rooms which will provide a "mind-blowing journey through the music, memories, and magic of ABBA!" (I came across this info on Strombergs' blog.)
The exhibit will include an interactive experience where people can get on stage with 3D holographic versions of the members of ABBA. You can see the cartoony-ABBA's on the SquareZero website. Square zero is the content provider of the the 3D experience. Musion Systems, the creator of the Musion Eyeliner high definition holographic video projection system, was another partner in this project.
Details about the holographic system can be found on the ABBAWorld website, along with the history of ABBA.