I must write a cross-platform real-time-strategy game within 2-3 months. I want use C++ and OpenGL and am looking for an engine.
The engine must be open source and work under both Linux and Windows. Preferably it should work with 3ds Max models. I do not know the game engines. Which engine would you recommend?
I know of three that still seem reasonably actively developed: Spring, OpenRA and Stratagus. Wikipedia has a list of open source game engines, some of which may be appropriate for an RTS game (such as FIFE, which used to bill itself as a Fallout-style engine, but should still be appropriate for RTS games).
Some of these engines may work directly with 3DS Max model files, but that file format (.3ds) is actually pretty archaic, cumbersome, and suboptimal for direct consumption by a game engine, so you may find that the engines instead support some other model format that Max can export to (or supply their own conversion tools).
Also, it's not open source (and does in fact cost money might cost if you need certain features), but people have used Unity to make RTS games as well.
Irrlicht is a great open-source 3D game engine. It doesn't have RTS-specific features but it could certainly be used to create an RTS (or any kind of game).
It's written in C++, runs on Windows or Linux and supports both OpenGL and DirectX.
Irrlicht is