QIX

[User summary]

You control a cursor able to draw lines on the screen. You may move along the edge of the screen and upon the lines you draw. You draw such lines in order to enclose areas of the screen (these areas become colored and unaccessible to both you and your foes). Once you have colored at least 75% of the screen, you advance to the next level.
You score points for each area you manage to color (you can move the cursor at higher speed to enclose the areas faster, but doing so halves the value of such areas).
Your enemies are other cursors moving on the borders of the screen or on the lines you draw (like you do, but they cannot draw new lines) and the terrible QIX (an entity represented by a bunch of colored lines that exists in the empty screen and move with variable speed and random patterns while also contracting or stretching).
The enemy cursors kill you by contact, while the QIX kills you by touching any line you are still drawing.
If you start drawing a line and halt, an extra enemy cursor appears at the beginning of such line and immediately chases you (hurrying you to complete the enclosing of the area... or to be annihilated by the QIX).
Successive levels get harder and harder (more enemy cursors, faster QIX, etc.).
You go on until all your "lives" are lost. Your goal is to score as many points as possible.