“SLiM is a Desktop-independent graphical login manager for X11” (slim)
You may add a preferred user to be auto-filled each time you start your computer – the username will be filled out, but you still have to accept, and enter your password.
But you may also auto-login by adding a new line below the default user:
Voila! I am unable to see this in the documentation – I got the tip from SliTaz forum – where I managed to enter the wrong email when I registered…. I had to register as firmitz…