1) A-Dock: a program that emulates Mac OS X's dock really well (no minimizing windows though). link
2) Mini vMac: because its the best emulator for the Macintosh Plus!!! link
3) Hypercard: enough said. Link
4) Apple Legacy Software CD not really app but it comes close, it has every apple II, III and lisa OS, the enitre macintosh os family from 1.1 to 8.1and every other piece of software that apple has put out up to os 9. Link
DiskDup+. The only application that will reliably read/write low density 3.5" disks for all Apple platforms as the IWM intended. http://www.macintoshgarden.org/apps/diskdup