Framelock knives available for sale. Part of the frame is cut out to slip in front of the knife blade when it is open, locking the knife. Push the frame lock out away from the knife (to the left usually), to unlock the knife.
From our Knife Encyclopedia:
The Frame-Lock has its origin in the Michael Walker Liner-Lock. Michael made this style lock a very useful one by adding the ball detent which pulls the blade down into the handle the last quarter inch or so and holds it in place. To overcome the "hold" created by the ball in the lock dropping into an appropriately sized and placed hole in the blade takes only a little force exerted by the movement of the blade using a nail mark, thumbstud, flipper, etc.
The Liner-Lock, as its name indicates, uses the liner to lock the blade in the open position. The Frame-Lock uses the same concept, but since there is no liner, a "locking bar" is cut from one side of the knife frame and is used in much the same way the liner is used to lock the blade in the open position. Chris Reeve is often given credit for inventing the Frame-Lock. He certainly was a very early user and popularized it in the Sebenza. A knife with this lock, which is stronger than the liner lock, is usually a premium knife with higher quality workmanship and materials than the typical liner lock. This lock is widely used by ourselves, Benchmade, CRKT and all of those using today’s modern designs and techniques for knife production.