As alternative to MECCANO (which is by design not for 3D-printing), there is STEMFIE — a fully free & open-source 3D-printable educational construction set.[0]
Another alternative: try reconstruct MECCANO parts in LDraw format for LeoCAD (LeoCAD has an option for export into STL).[1]
Thanks for the links, maybe I can still find the Meccano sets I used to have.. Should be interesting for those who want to mix and match with 3D prints.
The title is wrong. It is not free. The demo is free
> You can download and try the demo version of VirtualMEC. The demo version of VirtualMEC has all the features of the retail versions with some limitations: you cannot save or print models; you cannot playback/animate a model's building process. Once you have downloaded and installed it, you can practice the included Tutorial (you will find it in the Help Topics) that will guide you through the process of building the Scooter model shown above. You will realize how it is simple to build virtual models (and quite similar to build real ones). Then, you can decide to unlock the retail version of VirtualMEC, that enables you to build models as big as you like.
Also there are Meccano Kinematics[1] and Meccano Gilde Nederland[2] sites with a set of various mechanisms created using VirtualMEC app.
N.B. In 2009 VirtualMEC review by Douglas Carson published in Meccano Society of Scotland Newsletter #79.[pdf]
[0] http://www.virtualmec.com/content/models.aspx
[1] https://meccanokinematics.net/meccano/models/
[2] https://www.meccanogilde.nl/vm/demos.html
[pdf] https://www.meccanoscotland.org.uk/downloads/mag079_April_20...