Smaller, programmable chip alternative

Its so fun making projects including the arduino, but because i only have one arduino, i can only do one project at a time.

Now, my question: Is there some sort of small chip that you can put your arduino program on so it can run that program, and run your project, while you use your actual arduino for someing else?

Maybe, a smaller chip that can fit into smaller spots?

Is this the kind of thing you're looking for?

To program it you'll need a usb-to-serial interface similar to this one:

The two boards connected together are almost identical in behaviour to an ordinary Arduino Uno. The usb-to-serial interface may be removed after programming.

Depending of the size and nature of your project you could take a look at the Tiny family, mabe the Attiny85.

They can be programmed just like your Arduino and from the Arduino IDE, and you can use your Arduino as programmer (Arduino as ISP)
Coding Badly has described the members here:

As other's have mentioned there are other, smaller chips; however, you could also make use standalone 328p chips (http://www.mouser.com/ProductDetail/Atmel/ATMEGA328P-PU/?qs=K8BHR703ZXhdUS2n3IW%2FRCbkGfFwGBdvghYqeY7OU3o%3D) They are $2.50 each or about 10 for $20. Add a 16 MHz resonator at 10 for $2.4 (http://www.mouser.com/ProductDetail/ABRACON/HWZT-1600MD/?qs=H8AWquzS%2FlPX64bvW2s9zt%252bRypW0wMDMJ90RBx1ej%2Fg%3D) and a 10k resistor for the reset pin (http://www.mouser.com/ProductDetail/KOA-Speer/MF1-4DC1002F/?qs=klP8Go34dYH4X9ZSLqGsvttjzVn1wqNOXWM%252bMNSsOqQ%3D) at $0.60 for 10 and you have the makings of 10 standalone arduino's for about $23