Streets and Alleys Solitaire is a harder version of Beleaguered Castle Solitaire (as if that was necessary).
How can that be, you wonder?
It can be and is, because Beleaguered Castle starts with the four Aces already dealt for you. There is no such nonsense with Streets and Alleys Solitaire, whereas in this game the Aces start somewhere positioned within the Tableau.
Additionally, the first four columns each contain seven rather than six cards, which of course slightly increases the diffficulty level.
At one point I was attempting (for my own amusement) to add a sort of subjective difficulty scale to some of the games of Solitaire on SolitaireOnline.Org. I now play each game a few times, stick a finger in the air, and pronounce without reference to any particular scale.
Semi colon in their rules for Streets and Alleys Solitaire describe the game as 'a little tougher' than Beleaguered Castle.
I would say, it is 'considerably tougher', although this is of course very subjective and possibly to do with the cards that I was dealt.