Crazy Eights is the card game that Uno was built from. You play cards matching the top of the discard pile by rank or suit; eights are wild and let you nominate a new suit; if you can't play, you draw. First to empty their hand wins.
It's simple enough for children and has just enough strategy — when to spend an eight, which suit to nominate — to stay interesting for adults.
They're wild — you can play one on anything, and you nominate the suit that must be matched next. Holding one is insurance against being unable to play.
Uno is a commercial descendant of it with a dedicated deck and extra action cards. The core rule — match by rank or colour, wilds change the colour — is the same.
Yes — tap a card to play it. Nothing to install.