TSE is an acronym for the Trax Sequencer Engine. The developer, Pete Goodliffe releases software under the moniker 'Trax Software'. TSE was originally developed for a sequencing project provisionally titled TraxSequencer.
TSE technology dates from 1996. The first version took a pattern based approach to the song structure which limited it's flexibility.
TSE1 lead rapidly to TSE2 which was developed and improved between 1997-1999. This was targetted at the Acorn RISC OS architecture only, although in theory should have been fairly portable. TSE2 is a linear sequencer engine. You record snatches of music called Phrases, and then place them inside Parts which are further put into the Tracks of a Song. This approach was considerably more flexible and powerful that the TSE1 approach.
TSE2 found its way into several RISC OS products. The first generation of TSE2 powered the TraxSequencer product. Later revisions to TSE2 and the user interface lead to the product Anthem. At its release Anthem was acclaimed as a new powerful way of sequencing, challenging the accepted norm.
TSE2 based products were only available commercially. See the R-Comp website for more information.
TSE3 is a third generation project based on the experience of TSE2. It includes the same revolutionary functionality but takes it into a new generation of implementation. Based on experience with TSE2, TSE3 provides a robust and powerful engine with greater extensability and portability. It draws on experience with TSE2 use in it's partitioning of the sequencer engine logic, the application support logic, the platform specific interfaces and the application itself in the most appropriate manner.
The C++ code has been brought up to a much more modern standard, leveraging the STL and other appropriate language features.
The other major difference between TSE2 and TSE3 is the release conditions. TSE3 is an open source project, allowing it to be used with few restrictions. It has been designed to be used by as large an audience as possible; indeed to be the defacto open source sequencer engine.