Hitscan

All weapons of Team Fortress 2 which fire bullets use hitscan to test for hits, but use the particle system to draw the bullets on-screen.

Half-Life 2 has many hitscan weapons (weapons which don't actually fire bullets, but instead trace a line and spawn an explosion/damage at the end). Sometimes it is useful, however, to hitscan just to find where a line hits a wall/player/etc.