Public transport in Belgrade has been free since New Year's and this has its pros and cons. In many comments I read that this is the first such case in Europe (and in the world). This is not so.
This was commented on "Facebook" by Vladislav Panev.
In Luxembourg (the entire country) all types of public transport are free for both locals and foreigners. In Tallinn only for citizens of the Estonian capital.
We will see how good this is in the future.
When a service is free, it is not valued enough. It is also debatable whether it will reduce car use, which should be the goal.
For me, as a regular user of Sofia's public transport (with a year-long card for a long time), it is important that it is fast enough, clean and connected. And the price is extremely affordable.