SpreadsheetLight is free to download and use, with generous licensing rights. Source code of the library is also available.
If you’d like to learn more about how the internal code work and about Open XML SDK, consider buying the programming reference manual I wrote, or enrolling in a course I teach.
If you want the whole shebang, from the original strong name key used to sign SpreadsheetLight, to the Visual Studio project files and the test Excel files I use, you can have everything for USD 499.
This is contact-only, meaning you have to contact me to get the Premium version. It’s not lying somewhere out there in the Internet because I will only zip up whatever I have right then and send that to you. This means you also get any bleeding edge feature I’m working on at that moment.
Spreadsheet Open XML From Scratch
This reference manual teaches you how to create an Open XML spreadsheet from beginning to advanced, going from simple cell assignment to inserting images and tables. Get more details.
Spreadsheet Open XML Charts
This reference manual teaches you how to create charts in an Open XML spreadsheet, and how to change chart properties from setting titles to setting doughnut (charts) to explode to setting major/minor gridlines. Get more details.
OpenXML Spreadsheet Boot Camp
This course teaches you how to translate an Open XML spreadsheet (or modern Excel file) into actionable tasks. The main problem has been to identify which parts of an Excel file correspond to which Open XML SDK class and the kind of code needed. This course uses the Spreadsheet Open XML From Scratch as a reference textbook, and builds upon that information. Get more details.