AYUMiS is a project aiming to create a cross-platform MMORPG set in space. It is developed in C++ with ClanLib. It will give the player full control over the game universe, with no NPCs or pre-planned storyline. It attempts to give the player a full range of choices and open-ended gameplay.
SoapQuest1024 is a small written after reading "20 Open World Games" on Gamasutra and coming across "Adventure". It's a very simple tile-based game written in 1024 lines of Java. You can wander around the place, picking things up and using them on other things by walking into them. You can save the gameand go back to it later. It's fully data-driven, based on a simple CSV format, and has things like wandering treants and a day/night cycle with light calculations.