FreeSG

If you're on the lookout for a 3D engine software that doesn't come loaded with unnecessary features, FreeSG is a great pick. It's a portable high-level 3D engine that emphasizes generality and is built on Agar. The best part? FreeSG is available under a revised BSD license and is actively being developed.

One of the things that sets FreeSG apart from other 3D engines is that it's designed to be an integrable component. While most 3D engines are application frameworks, FreeSG is built for integration in a wide range of applications, offering greater flexibility when it comes to hardware platforms.

When developing FreeSG, the aim was to implement a set of efficient algorithms that cater to a wide range of hardware and applications. This means that the speed and memory tradeoffs can be adjusted for a range of applications, from polygon-restricted games to massive simulations that require photorealistic rendering using the latest graphics hardware.

It's worth noting that FreeSG is licensed and distributed under the terms of the BSD License. If you're looking for a lightweight, functional 3D engine that doesn't weigh down your system with unnecessary features, FreeSG is definitely worth checking out.