The current version of Nestopia features * Completely free to use. * Efficient CPU usage, for improved battery life on PowerBooks. * Flexible video display sizes with numerous Blitter effects. * Sound recording functionality. * Transparent decompression of GZIP-compressed game files. * Support for 174 different mappers. * Support for five additional sound chips. It is THE BEST cycle-exact emulator for NES on OS X. The previous reviewer who said Nestopia can't run full screen stated falsely. The free version of Nestopia cannot run full-screen; with the purchase of Emulator Enhancer (which works with ALL of Bannister's 28 current emulators). From his web site: Additional Features This feature set above can be expanded using Emulator Enhancer, a shareware module which adds the following additional options: * Full screen mode. * Network play (some emulators). * Real time video and sound filtering. * Support for USB game pads and joysticks. EE is currently available for . If anyone wants to rate EE (based on the customer having to pay for it), this belongs in a review of that software, not Nestopia. Nestopia even has its own support forum now; use it if you need help with the program: http://www.bannister.org/ubb/ultimatebb.php?ubb=forum;f=36 I rated the Features as low, as Nestopia is missing a few features in the free version -- also, it is currently missing support for zip and 7-zip archives, as well as for Quartz effects and OpenGL overlays. Everything else, I rated as 5, as there are no other NES emulators that perform as well (on ANY platform) as long as you have a fast enough CPU to run it at full speed.