Wearable camera maker iON Worldwide was once GoPro‘s (NASDAQ: GPRO) largest rival. iON controlled 12% of the global action camera market in 2014, according to IDC, compared to GoPro’s 48% share and Sony‘s (NYSE: SNE) approximate 8% share. However, iON recently filed for bankruptcy, stating that its revenue declined from $25 million to $12.4 million between 2014 and 2015, and that it was $15 million in debt.