Independent Bingo Sites
A lot of bingo sites can be termed "independent" but in this instance we're referring to the bingo software that they're using to power their sites. These are usually big brands in their own right, for example Tombola, or who have developed a unique product such as BingoCams. Not all independents enjoy success. Amuso.com for example tried to 'go it alone' but quickly came unstuck whilst Wonder Bingo found that the transition from social to real bingo room wasn't fruitful.
It's worth noting though that many sites that use software platforms run independently from other sites using the same systems.