The vast majority of bingo sites out there at the moment are based on some kind of standard software package which, amongst other things, gives the operator of the site a certain amount of security.
With this security however comes a lack of flexibility and thats where proprietary software comes in.
Proprietary software simply means that the operator of the site has chosen to develop their own bingo software independently instead of buing one in an off-the-shelf fashion.
The major downside of this is the huge investment in time and resources that is required to create bingo software from scratch.
The upside is that the operator gets exactly what they want in terms of every aspect of how the site works and how it looks.
An additional upside is that if the end product is of a very high standard, it can be packaged up and sold to other operators which will hopefully offset some of the development costs.
This does not always happen however and sometimes the software just stays in one place on one site and never gets used by anyone else.
Generally speaking, if the team who developed the custom bingo software have done a good job then the site it is created for becomes a great success and players enjoy playing bingo on it.
If however the process does not go well or is not completed fully then this can result in a poor bingo site which in turn results in a poor user experience and usually the evential closure of the site.