What engine are you using?
Project::OSiRiON uses its own engine, it is written from scratch in C++ and uses SDL, OpenGL, OpenAL, libjpeg, libpng, zlib and the Bullet physics library. It is a work in progress and evolves with the game as required.
Is this a singleplayer or a multiplayer game?
While it is possible to run the game in singleplayer mode, it is intended as a multiplayer game. Singleplayer mode is essentialy like playing alone on a server. A real, story-driven single player campaign is a long term objective and is not planned for release 1.0.
Why are there no weapons?
There are. You have to buy them at a dealer and mount them in the inventory window.