If you like to play around with micro controllers you know this hustle: You want to test a part of a program and first you need to completely wire up the uC on the bread board.
Not with these handy parts any more!
These are complete programmable micro controllers that could be stuck to any solderless breadboard. Easy to program and easy to interface.
The big advantage is, that you don't need double side PCB, you don't need a custom PCB at all, you can also built it with common bread board and some wires too.
Step 1: The schematics
The basic interface to program a micro controller is rather easy.
You need the power sources.
Then you have to tie the reset pin high, with a pushbutton to reset the uC.
And finally you need the three other lines to program the uC, Mosi, Miso and SCK.
I will explain this for the Attiny2313, but other uCs are as easy as this.
In the pictures to this step, you find the most simple schematic, then one with the ISP socket and the last one with all the pins routed to pin headers.