A few links as I'm thinking of it for some of my favorite construction systems / building components. To clarify what I mean, these are systems of generic parts that are compatible with each other and usually used to build something else. Hopefully if that's not clear the examples themselves will clear things up.

What is Contraptor

Contraptor is a DIY open source construction set for experimental personal fabrication, desktop manufacturing, prototyping and bootstrapping.

Print/export
Toolbox