Another day, another tragedy...
1,5 half year later 2 devs were able to deliver :
- custom authentication. Basically they did a very simple client credentials grant.
- a custom wrapper to manage windows services
- a custom job scheduling system
- a custom logging library to log everything to windows event viewer!!!!!!
- all csv reports are created using string interpolation WriteLine("'{varA}','{varB}'") like this...

There are a lot of defects in those functionalities and they delivered almost 0 business features.

Console.WriteLine (for C#, System.out.println for Java), because that will always be one of the best debugging tools.