So... / Therefore... / And so...
Very common informal connector introducing a consequence or conclusion. More casual than por lo tanto. Así que + indicative.
It was raining, so we decided to stay at home.
We didn't have tickets, so we couldn't get in.
—What will you do? —There's no other option, so I accept it.
I'm tired, so I'm going to sleep.
There was nobody, so I left.