Turning R scripts into a "data science tool"
You can refer below the answer to the similar question asked.

https://stackoverflow.com/questions/14096520/compile-r-script-into-standalone-exe-file

Alternatively,
You can use R-shiny app for it. You can build application which can be deployed on website also. See below link for the examples of application made by R-shiny.

https://shiny.rstudio.com/gallery/

This way client will not be seeing your code at all and will be working on it just as a tool.