Can you help me identify simplest naturally occurring self-replicating molecule? Or even better, let's make one artificially... where "self-replicating molecule" is such that contains at least two different atoms, it reacts with other atoms and molecules so that it accumulates duplicates of those atoms it is composed of, and then at some point reaches "critical mass" (length, or something) where it splits into two identical molecules. This question was inspired by http://organicbuilder.sourceforge.net/ - "This freeware demonstrates an artificial chemistry. Each circle is an atom, that floats around and can become bonded to others to form a molecule... Perhaps the coolest thing you can do is template replication - the process DNA uses to make copies of itself. If you choose the right rules you can actually get this working - follow through the challenges to find out how." I find that little simulation is amazing, and pretty cool as a game too! Surely then we should be able to do it with real atoms as well, right? What software would be best for exploring solutions to this puzzle?