There is lots of Apple II software on the internet! Here are some of the most relevant websites:
http://www.apple2.org.za/mirrors/
Mirror of many Apple II software repositories
Virtual Apple ][
An extensive Apple II game library
To install a disk image in the AppleIIGo Dashboard widget flip to the back side of the widget, click on the Disks button, and copy your disk image to the folder that just opened in Finder.
Author's favorites
Lemonade Stand
Apple's first game
Arkanoid
The classic break out game
Defender
Another console classic
TETЯIS 2
Stack it up
The Hunt for Red October (Disk 1)
(Disk 2)
Submarine sim
Oregon Trail (Disk 1)
(Disk 2)
Make it to Oregon in the 19th century