Our server is Survival at the very base level, but with a few major changes to the way the world is split up. We have five different 'regions', which act very like countries. Each region would have a 5000x5000 square inside the server, and would have one monarch ruling over it. The region's players would elect 5 'MPs' (very similar to the UK government) to sit with other region's elected players in a sort of assembly, to create server-wide decisions, such as rules.
  When players join the server, they will be automatically assigned / allowed to choose a starter region. They will only be allowed to build and work here. As they progress through levels, and earn more money, the players will be able to apply for passports or citizenship of other countries. They will then be allowed to build and work in the new one.
  The monarch of each region can be overthrown if they are killed by another player. The new player will take over and be able to drastically change the region-specific rules.
  Each region or country will have a specific theme, where the players work for that category to export products, perform services etc. to earn money for themselves. They could pay income tax on everything they earn to the government, which will allow the country to expand their territory into the 'wasteland' (the area of the server outside the 10000x10000 border of the regions), or invade other countries and declare war on them to conquer their land. The regions will be able to create embassies in other countries to provide support for stranded players, and to develop relationships between different regions.
  Every month, the top X members in each region will be rewarded and the country will grow stronger. There will be multiple categories for each country's power, such as total combined player Vault balance, or percentage of blocks claimed.