Half-Life
Half-Life: Opposing Force
Half-Life: Blue Shift
Half-Life 2
Half-Life 2: Episode 1
Half-Life 2: Episode 2
Portal
Portal 2
Half-Life: Alyx
Here is a comprehensive list of all Half-Life games made by Valve from 1998-2020.
Half-Life
Half-Life: Opposing Force
Half-Life: Blue Shift
Half-Life 2
Half-Life 2: Episode 1
Half-Life 2: Episode 2
Portal
Portal 2
Half-Life: Alyx