The Pen is a classic prison server that feels like the 2014 era. It is barebones and grindy and it does not hand you overpowered armor. You mine and you smelt ores yourself and you do risky runs through PVP zones to sell if you want money.
You rank up from A through H and then you can reach Parole. After you finish the main ranks you can keep going with a prestige system and you can pick how you want to progress.
Mining is the main path with old school prison grinding and better mines as you rank up. Fishing is a full custom system that can earn good money per hour with unique rewards and boosts. There is also a mob arena where you fight waves and bosses for group rewards plus money and shards.
There is a cookie farming bakery system too where you farm wheat and cocoa then bake cookies with custom mechanics. You can do long term cookie quests compete on leaderboards and turn baked cookies into higher tier rewards.
The server also has guards enforcing contraband rules and illegal crops for high risk high reward. You can rent cells and plots use an auction house do bounties try parkour and run player shops. Premium stuff is not required since anything paid can also be earned by playing.

