Ludum Dare is a worldwide game jam where games are made from scratch in a weekend and Ludum Dare 49 will be running from the 1st to the 4th of October (that's f...
The idea of Ludum Dare (as said in the first line of the post) is to make games from scratch in the jam.
Take a look at the rules: ldjam.com/events/ludum-dare/rules