BetterChests

For more in-depth discussions, there is a discord-server available.

This mod was created during ModJam Aug. 2013. Modjam is basically a 92 hour ModMaking competition. Out of 20 Single-Modder-Mods, it was rated to fifth place.

It is about a chest, that you can upgrade to how you want it to be. You can make a cobblestone generator out of it, you can make the chest suck in nearby items, or you can use the chest as a big furnace, a farm, a mob farm, an animal farm and so on. Of course, you can also make the chest bigger on the inside. There are many more upgrades, but you should discover them yourself.

There is also a backpack you can use, that can accept (mostly) the same upgrades.

Note: Older versions can be found here.