Just makes all iCalendar events from transparent to opaque (busy).
I use it on Google Calendar for my university lectures. The university's iCalendar publishes all events as "transparent events" and Google Calendar shows my status as "Not Busy" during classes.
docker build . --target build-image -t busycal
sudo docker run busycal --bind 0.0.0.0:8000
The new iCalendar link will be: http://127.0.0.1:8000/?ical=<ical_url>
You can protect the endpoint with a token by setting the enviroment variable BUSYCAL_TOKEN to a token of your choice. After that you just add to the request url the query parameter token=<BUSYCAL_TOKEN>.