Do you wish you could change the rules of the game? Well now you can with the gamerule command. 

/gamerule keepinventory true makes it when you did you keep your stuff

/gamerule dodaylightcycle false stops the sun or moon going down.

/gamerule sendcommandfeedback false stops telling everyone you used a command.

/gamerule commandblockoutput false stops command blocks from spamming you

/gamerule mobgriefing false stops creepers endermen and ghast from breaking blocks

/gamerule doweathercycle false stops the weather from changing vital

/gamerule dofiretick false stops fire from breaking blocks

/gamerule PvP false stops players from hitting each other 

/gamerule showcoordinates true tells you where you are by the exact block

/gamerule tntexplodes false stops tnt from exploding

/gamerule naturalregeneration false stops you from regaining health

/gamerule firedamage false stops you from taking damage from fire

/gamerule falldamage false stops you from taking fall damage

/gamerule doinsomnia true gives you insomnia

There are a lot more so find them and see what they do