You need the nightly rust compiler to run the server, you can get the rust installation tool rustup at rustup.rs
To install nightly run
rustup toolchain install nightly
When the nightly toolchain is installed you can install keydisp with
cd server\keydisp
cargo install
Run keydisp. Press F10 to select the current foreground window. Then navigate to index.html, it should display keyboard input from the selected window.
To use with OBS add index.html as a browser source to OBS.