ABBA Singbox is a sing-along ABBA app for iPhone. The app's description makes no bones about its inspiration, citing console games SingStar and Lips. As with those, you sing along to the songs, with two difficulty levels. Amateur mode merely rates your timing, while Pro mode also assesses your pitch.
You can publish your score on Facebook, but it can also be uploaded to ABBA's official website and Facebook group, to see how you stack up against other fans around the world.
For £1.79 you get the app and one included song: Dancing Queen. However, to get the other three songs - The Winner Takes It All, Mamma Mia and Gimme, Gimme Gimme (A Man After Midnight) - you'll have to pay £1.19 a pop through in-app payment. In other words, that's a total of £5.36 for the app and four songs.