Algodoo

16,777,216 meters from the center of the simulation. That's about seventeen thousand kilometers, or 10 thousand miles (a 1:1 scale model of earth can fit inside this simulation with a bit of room to spare, enough for the moon!
the reson the graph ends here is that the coordinates of anything are represented as x = (24 bit binary number), y = (24 bit binary number). The decimal point is shifted at each power of 2 to reduce overflow and increase simulation space. Because of that, at each power of two, precision is lost in the form of less decimal points. at the 24-bit overflow point, the precision has been reduced past 1 meter. here's why that happens.
lets say we have an object at [000000000000000000000000, 000000000000000000000000]. this is binary for the origin. when the object moves out of the origin, like 1 unit to the right, a decimal point appears in the coordinates. [1.00000000000000000000000, 1.00000000000000000000000] at each power of two, this point needs to shift so that the system does not overflow. when a coordinate passes 1.11111111111111111111111 (1.999...), the decimal shifts at a loss of decimals and a gain of space inside the simulation. 1.11111111111111111111111 turns into 10.0000000000000000000000. after 111111111111111111111111111111111111, the simulation breaks down. the precision has been reduced to a meter and the graph disappears. i have not reached into the code myself, but i found this because minecraft uses the same type of code to coordinate everything, and after a certain point, precision has been reduced to a meter and the stripelands develop, which is an area of meter-wide stripes of grass. This, however, happens twice as far in minecraft.