I think most people who have used a BBT or anything similar know that the main thing you are really paying for is the data subscriptions. While an open source solution would be amazing there is no incentive for anyone to provide you with real time data. Without the vast number of resources that an actual BBT can pull in you just have a charting software with a Twitter feed. At the end of the day the yearly cost of a BBT is surprisingly justifiable if you have the need for real time data for some use case like quick arbitrage trades. However, most people who would want to use this probably want to day trade and chase the market which is an awful idea and will likely lead them to spending more money on data and psychiatrists than they would have ever made on the market.