wfassoc: Core Rust library. Rust programmer can directly utilize it.
wfassoc-cdylib: A dynamic library exposed for C/C++ and other languages users.
wfassoc-exec: A executable configuring file assocation according to user given profile and request.

If you are a programmer who just want to silently set your file associations for user, wfassoc-exec would be your best choice. The only thing you need to do is that write a manifest TOML file, and provide it and wfassoc-exec with your executable. By executing wfassoc-exec with this TOML file in your executable, you can simply achieve this goal, by analyse its return value to check whether it success.

However, if you are prefering that let user decide which file associations should be created, even have an UI displaying all current file associations related with this program (like 7-Zip File Manager does), you can choose wfassoc-cdylib as your solution. wfassoc-cdylib exposes all essential functions for this task. And you can build it with your own program.

At last, if all scenarios above can not cover your requirements, you can utilize wfassoc directly in Rust, change all essential code in your favor, and finally produce the artifact which only works for your requirements.

For the usage of these projects, please browse their README respectively.