The Pen MC is a classic prison server that feels like the 2014 style. It is barebones and grindy and you do not get overpowered armor right away. There is no instant selling so you mine then smelt your ores and you have to travel through pvp areas to sell and stay alive.
You rank up from A to H and then you can reach Parole. After you max out you can prestige and pick different ways to keep progressing. You can stick to mining or go into a custom fishing path or fight waves in a mob arena with boss fights. There is also a bakery setup where you farm wheat and cocoa then bake cookies with custom mechanics and do long term cookie quests and leaderboards.
It also has illegal crops that are high risk and high reward and there are guards that enforce contraband rules. You can rent cells and plots and use an auction house plus player shops. There are bounties and solitary confinement and some parkour challenges too.
The server says premium stuff is not pay to win since everything you can buy can also be earned by playing. It is more about the grind and economy balance and long term progress.

