Ummm...maybe it's just me but your question seems to be asking something so general that there isn't really an answer. Digital design involves designing circuits with digital components like logic gates, microprocessors, microcontrollers, RAM, FLASH, ROM, and everything else that processes information using digital signals. Analog is everything else (especially radio, audio and power supplies). But these circuits can incorporate digital components too. And digital circuits can still involve analog design when you really start to push the limits since the world is by nature analog (things like noise, ringing, EMI, RFI).
For tools...
oscilloscope - analog (but can be used for digital and be used to observe analog aspects of digital signals)
logic analyzer - digital only
function generator - analog
serial protocal analyzer - digital
frequency counter- digital or analog