Games like Diplomacy is Not an Option: Shareware
Games like Diplomacy is Not an Option: Shareware include They Are Billions, Frostpunk, Manor Lords, Kingdoms and Castles, and Farthest Frontier. We matched them by the tags players give Diplomacy is Not an Option: Shareware on Steam (Strategy, City Builder, Colony Sim, Tower Defense, and RTS): closest matches first, and among equally close ones the better-known games.

They Are Billions
Shared: Strategy · Colony Sim · Base Building

Frostpunk
Shared: City Builder · Strategy · Colony Sim

Manor Lords
Shared: Strategy · City Builder · Base Building

Kingdoms and Castles
Shared: City Builder · Colony Sim · Strategy

Farthest Frontier
Shared: City Builder · Strategy · Building

Kingdom Two Crowns
Shared: City Builder · Tower Defense · Strategy

Stronghold Crusader: Definitive Edition
Shared: Strategy · City Builder · Colony Sim

Against the Storm
Shared: Strategy · City Builder · Base Building

Workers & Resources: Soviet Republic
Shared: Strategy · City Builder · Base Building

Banished
Shared: City Builder · Strategy · Colony Sim

Prison Architect
Shared: Strategy · Colony Sim · Building

RimWorld
Shared: Colony Sim · Strategy · Base Building

Stronghold: Definitive Edition
Shared: Strategy · City Builder · RTS

Becastled
Shared: Strategy · City Builder · Base Building

Thronefall
Shared: Strategy · City Builder · Tower Defense

Foundation
Shared: City Builder · Strategy · Medieval

Empires of the Undergrowth
Shared: Strategy · City Builder · Colony Sim

Oxygen Not Included
Shared: Colony Sim · Base Building · Building

Stronghold Crusader HD (2012)
Shared: City Builder · Colony Sim · Strategy

Ostriv
Shared: Strategy · City Builder · Colony Sim

Dwarf Fortress
Shared: Colony Sim · Strategy · City Builder

Going Medieval
Shared: Strategy · Colony Sim · Base Building

Norland
Shared: Strategy · City Builder · Colony Sim

Stronghold HD (2012)
Shared: City Builder · Colony Sim · Building