This is the LitDev extension for Small Basic version 1.2.
See http://litdev.co.uk for alternative download, additional details, online documentation and source code.
The source code is also available on GitHub.
As with all Small Basic extensions, copy the extension dll and xml (inside the download zip) to a lib sub-folder of the Small Basic installation folder, usually in one of the following locations:
C:\Program Files\Microsoft\Small Basic\lib
C:\Program Files (x86)\Microsoft\Small Basic\lib
You may require to create the lib folder if it doesn't exist.
If the extension commands fail to appear in Small Basic (type LD and no options appear) then you may need to unblock the downloaded dll. Right click LitDev.dll and select Properties and clear the block if present. Alternatively, unblock the downloaded zip file before unzipping the content.
Copy all other files (documentation and samples) elsewhere.