USBasp is a USB interface adapter for ATMEL ISP.

This is a cheap programmer.

Some boards contain jumpers to disable power delivery to the target device, otherwise they always supply power.

SUBSYSTEMS=="usb",\
    ATTRS{idVendor}=="16c0",\
    ATTRS{idProduct}=="05dc",\
    MODE:="0666"

Generic USBASP comes with an old firmware, you can upgrade it using a USBtiny like this

avrdude -c usbtiny -p atmega8 -e -U flash:w:usbasp.atmega8.2011-05-28.hex

$ avrdude -c usbasp -B 5 -p m328p -D

avrdude: set SCK frequency to 187500 Hz
avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.01s

avrdude: Device signature = 0x1e950f (probably m328p)

avrdude: safemode: Fuses OK (E:FD, H:DA, L:FF)

avrdude done.  Thank you.

Project page

Schematic

Updated firmware