From Just Solve the File Format Problem
ToolBook was authoring software for creating learning systems. Developed by Asymetrix, was later merged to form SumTotal Systems. Discontinued on December 31, 2021
ToolBook 1.0 was released in 1990 and the last version 11.5 was released in 2012. 
- TBK are ToolBook Books. Earlier versions begin with hex values
034A424F, but later versions use the Portable Executable format to store their data.
- SBK are System Books containing scripts. Same format as TBK files.
- TBKX are ToolBook files save in an ZIP container in XML format.