Universe is an Open-Source game which resembles Master Of Orion. It is written in Java. The goal is to have as few arbitrary limits as possible, allowing games as large as you wish. It also supports a concept called "Schemes" which allows programmers to develop distinct rule sets and extensions.
GEMpire is a simple turn based multiplayer strategy game, written in java, designed to be played over the internet in client-server fashion. It is a generalization of the commercial game Empire Deluxe for the PC. It consists mainly of a server, a client, a map editor, and a random map generator.
XiStrat (aka 'Extended Strategy') is in particular about turn-based, networked multiplayer, non-cooperative, zero-sum, abstract strategy board games (e.g., Chess, Go, Reversi variants, etc.) on 3D-visualized polyhedra and contains a server, client GUI, autoplayer engine, utilities, and documentation. Related recreational modern mathematics (single agent, cellular automata, graph/group/complexity/knot theory, discrete geometry, algebra, combinatorics, and mathematical physics) is also dealt with.
Colossus is an attempt to create a Java clone of Avalon Hill's Titan, an out-of-print fantasy wargame. The main goal is networked multiplayer, allowing Titan players to more easily find opponents (networking works, but is not very robust yet). There is a working but not very strong AI, and in addition to the standard game, Colossus includes support for several variants.