In RPG Maker, when you defeat enemies in battle, everyone that's alive will receive some EXP.
So for example, if you defeated a slime, and the slime is worth 100 EXP, then every party member that is alive will receive 100 EXP. If you had one member, that member would receive 100 EXP. If you had four members, then all four members would receive 100 EXP.
However, this means there is no incentive to try to challenge yourself to have one party member solo the battle, because there's no difference whether you bring your entire party or not.
This plugin changes the way EXP is rewarded. Instead of simply giving everyone the same amount of EXP, the total EXP is divided among all of the party members.
For now, the EXP is divided equally, so if an enemy gives 100 EXP and you bring three other party members with you, then everyone will only receive 25. However, if you decided to solo the enemy yourself, you will get the full 100.
More information and downloads available at HimeWorks