Earth and Sky is an interactive fiction trilogy written by Paul O'Brian about the adventures of a brother and sister who gain superpowers while searching for their lost parents. The first part, Earth and Sky was entered in the 2001 annual Interactive Fiction Competition where it finished eighth. The second part (Another Earth, Another Sky) was considerably more successful, winning the competition in 2002 as well as picking up the 2002 XYZZY Award for Best Use of Medium. The third part, Luminous Horizon, also managed to win the Interactive Fiction Competition when it was released in 2004.
Source: Wikipedia, "Earth and sky", available under the CC-BY-SA License.