There is a Minecraft mod called Project E. The original version was called Equivalent Exchange. It allows you to craft a "transmutation table" that you can use to convert objects into energy, and the energy back into objects. Different objects are worth different amounts of energy. You can store the energy for later, but you can only create objects that you have converted once before.
This mod completely changes the game. You only need to find or craft one of any given item in order to create an arbitrary amount of them, limited by the amount of energy you have stored. Many modded items do not get assigned energies (for various reasons), and so become either completely worthless (as you can't get any energy from them), or much more difficult to acquire than the average item (because you can't just create them with energy).
There are devices which generate energy. They cost a relatively large amount versus what they generate. The game here becomes: how much am i willing to skim off my energy reserve in order to increase the rate at which i accumulate energy. The curve is exponential. Every device you add reduces the time required to build another device.
There are also glitches that let you generate energy much faster. Item processing exploits, such as grinding up a blaze rod into two powders, and then reconstituting it into two blaze rods. With the right combination of mods, you can create a machine that generates more energy in a couple of minutes than you can even expend.
It's a fun mod. There are items of great power that are incredibly expensive. But at a certain point, there is nothing left to do. There is a big wall at the end of the fun. Everything in the game has been reinterpreted in terms of energy. The function of items no longer matters, only the number associated with them. Your powerful items shield you from such basic concerns as walking or farming. You do not need to explore because you already located every valuable item and stored it in your transmutation table. You have already crafted everything (exactly once, and transmuted it into energy, and pulled out eight of them and crafted them into the next tier of material, and transmuted it). All of the normal motivation loops are broken. You are no longer playing Minecraft. You are playing Project E.