Coracle is a game designed to improve corner lookahead by testing your ability to identify partially visible corners.
Look at the two corner stickers to identify the corner and then click on the corner in the exploded cube below. If you're not used to the default orientation of the cube, click on the arrows to turn the cube to your desired orientation. Keyboard controls may also be used to improve speed.
If you're not interested in identifying pieces in which U stickers are visible then check the 'NOU' option. This is useful if you're training for F2L lookahead only.
If you're just starting out, it may be useful to concentrate on one corner location at a time. Use the checkboxes marked L, R, and D to control which corners are shown.
Your personal best time is recorded at the top of the page next to the heading PB. Simply click on the time to clear it.