I started a bug tracking project because every development team needs a good bug tracking application. Since I'd like to sell two things - myself and .NET smart clients - creating an application that development teams use every day seemed like a natural fit.
Besides, I agree with Joseph Jones, nobody has gotten bug tracking right yet - primarily because every development team wants something different. I also agree with Joel Spolsky. You shouldn't make your bug tracking too complex. But a lot of teams build their own bug tracking application because they want the option to add features. Those are the teams I created Satyr for. I'd like to give them a solid foundation to build on.
However any team that chooses Satyr to save money is deluding themselves. Building your own bug tracking application - even if it is based on a solid foundation - will not be cheaper than buying a professionally developed and supported solution. Before you decide to build your own make sure you understand the tradeoffs.