I just realized that there is a way to get free gold (other than a free chest) that can also give a bit of XP. However, this doesn't involve any jailbreaking, and once you are in the later levels, it is an incredibly slow way of acquiring gold. This is meant just to be used as an informative blog.
This is gold farming.
Gold farming in general is described as a method of repeatedly acquiring gold through a same way. In Clash Royale, this involves donating, a clan, and two accounts.
The steps are relatively simple:
Make sure there are two accounts. Log on both of them. Make them join a same clan. One would request for a rare card. The other account would simply donate the rare card, making him/her earn 50 gold. Then, the person that donated the rare card would request the same rare card. The other person would donate the rare card, making him/her also earn the 50 gold. This would make no difference in the cards, but both players would earn 50 gold and a couple XP.
Attached is a photo that shows this: