RepRap was kind of the mother of all 3D printers that reproduce themselves. Most of the 3D printers that were made for the home-use are a modified version of a RepRap 3D printer. Dollo 3D uses more 3D printed parts than RepRap and less other mechanical parts.
RepRap 3D printers typically use 3D printed connections for the frame of their printers. To move the printer stepper drivers are used. For the Z axis it is common to use a threaded rod and belt drives for the X and Y axis.
Dollo 3D uses a completely different concept: They have constructed a 3D printer that uses only 3D printed parts and an E3D metal extruder. The frame looks like a kind of cube with Lego parts. All parts can easily be connected and disconnected and the extruder is moved with stepper drives too. But they don’t use any beld or threaded rod for their printer – only 3D printed parts. However, the Dollo 3D kits are not cheap – for 250$ you will get a roll of plastic and all electronic components. For 350$ you will get the printed parts and all electronic components. If you browse for more information on the internet you will also find RepRap 3D printers like the Prusa i3 starting at the same price.
The Dollo 3D can be easily enlarged because you can print all the needed parts and simply stick them together. The question is how stable the frame is when it gets bigger. On the Kickstarter website of the project even CNC milling is listed as a possible use case for the frame – that seems a little bit unreasonable. If the Dollo 3D will be successful one can’t be predicted right now. The crowdfuning campaign has the goal of 50.000$ and will end in 25 days.
If you want a more detailed look at the printer, all files are available on GitHub.