Mars

Mars was habitable.
Mars had liquid water flowing on its surface back then, and single-celled lifeforms might have formed at the same time as they formed on Earth.

Mars didn't have oxygen in its atmosphere or grow grass, so it kind of looked like the present version of Mars with a few oceans of water covering its surface. Mars had a thicker atmosphere than today and warmer temperatures, and it was just right for life until the Sun blew away most of Mars's atmosphere, exposing all the lifeforms to the freezing cold.

Mars had just one natural satellite back then.