I have made this charlieplex rgb led cube...
http://aglick.com/charliecube.html
And found this link...
Now my question is how difficult is this to program a Pic 16f688 which I have instead of the AtTiny 84 which I don't have.
I may need another Tiny or suitable programmer.
The Pic 16f688 and AtTiny 44/84 are both 14 pins chips but pinouts may not match.
The site you link to shows sketch code for standard Arduino's the ATtiny84 will not do it as it's a few pins short of what's needed and probably short on other internals like timers.
As to the PIC I don't think your going to have much luck porting the code over to it (assuming the PIC has suitable number/type of pins needed). Probably easier to buy a Leonardo or other compatible Arduino.
You can do this with any arduino that has 16 or more tri-state I/O pins (uno, nano, mega, ...).
gregted:
Now my question is how difficult is this to program a Pic 16f688 which I have instead of the AtTiny 84 which I don't have.
You're asking in a Arduino forum...?