imports from backlog, synchronization with osgameclones

entries/crystal_space_3d_sdk.md

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+# Crystal Space 3D SDK
+
+_3D framework._
+
+- Home: http://www.crystalspace3d.org/, https://sourceforge.net/projects/crystal/
+- State: mature, inactive since 2015
+- Download: https://sourceforge.net/projects/crystal/files/
+- Platform: Windows, Linux, macOS
+- Keywords: framework, 3D
+- Code repository: https://github.com/kyanha/crystal.git, https://svn.code.sf.net/p/crystal/code (svn)
+- Code language: C, C++
+- Code license: LGPL-2.1
+- Code dependencies: OpenGL
+
+## Building
+
+- Build system: Make