Spider Solitaire uses two decks and asks you to build eight complete sequences from king down to ace, which are then removed from the table. Cards stack in descending order regardless of suit, but only a run of the same suit can be moved as a group — which is the constraint that makes it hard.
When you run out of moves you deal ten more cards across the columns, whether you're ready or not. Managing the board so that deal doesn't bury everything is the real skill.
Because only same-suit runs can be moved as a group. Building a mixed descending run looks like progress but produces a stack you can't relocate, which is how most games lock up.
One suit is a gentle introduction, two is the standard challenge, and four suits is genuinely difficult — most deals at four suits are lost.
Yes — tap or drag cards. Nothing to install.