it's a powered switch that latches on and off with a momentary spst mechanism.
the capacitor and the p fet gate charge up to rail voltage. the load is off, but it's grounded, so it pulls the N fet gate off.
when the button is pushed, the N fet gate goes high from the capacitor charge and it turns on. this pulls the P fet gate low, and it turns on too. the cap discharges slowly through both the N fet and the load.
when the button is released, the voltage on the load holds the N fet gate up. the fets are now latched on.
once the cap has discharged, pushing the button again pulls the N fet gate down, which turns off, blocks the p fet gate and sends it high, turning it off too. the switch is now off!
http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/electronic-circuits/push-button-switch-turn-on/latching-toggle-power-switch
from fiddling about in the simulation I found that it gets pretty touchy about the load so it might not be suitable for all loads. also it doesn't latch on if you hold the button too long
