func_pushable

Spawnflags

SF_PUSH_HOLDABLE	512 (the player can pick up and carry the object, as in Half-Life 2)
SF_PUSH_BSPCOLLISION	1024 (use the object's precise shape instead of a bounding box for collision testing; a good choice for making a boat, for example)

The SF_PUSH_BSPCOLLISION spawnflag not only used the object's visible physical shape, but also lets a func_pushable move other objects placed on top of it. Examples can be found in demo maps.