In the main code page of this github page it says:
A CalDAV server like [Baïkal](http://baikal-server.com/), [DAViCal](http://www.davical.org/), [Radicale](https://radicale.org/tutorial/), etc
the baikal link leads to an ad infested landing page instead of an actual homepage for baikal.

searching for it, it looks like the link for baikal should be:
https://sabre.io/baikal/
as per the sourcecode repo on https://github.com/sabre-io/Baikal

Also, the Radicale link on the same line is 404 errorr. instead of:
https://radicale.org/tutorial/
it should be
https://radicale.org/

the Doctrine DBAL link is also dead. and should link to
https://www.doctrine-project.org/projects/doctrine-dbal/en/4.1/index.html