I'd start with the free ones: http://www.zachtronics.com/the-codex-of-alchemical-engineering/ http://www.zachtronics.com/the-codex-of-alchemical-engineeri... h

I'd start with the free ones: http://www.zachtronics.com/the-codex-of-alchemical-engineering/ http://www.zachtronics.com/the-codex-of-alchemical-engineeri... http://pleasingfungus.com/Manufactoria/ http://pleasingfungus.com/Manufactoria/ Then depending on which one (or which parts) you like the most, select a similar one