People, does it exist any open source project to print with continous carbon fibers (or other fibers) as in markforge mark 2 commercial model?
Not…yet.
Yesterday I tried to print with Kevlar fibers. It failed miserably:
missing/deleted image from Google+
…and yet, @ChPech it is attempts like yours that continue to push the boundaries of 3D printing technology. So, thank you for trying. 
Not yet. But it won’t take much to modify a dual extruder machine to do it. I’ve used the markforged, while impressive, the "onyx " material is the most useful by far. You can get it under other names and use in most all printers
Start with high temperature abs(270c) first and work your way up to pc, nylon and then Kevlar. Most of the materials are modified version of the original so thats another challenge. Zortrax and Ups printer are the obvious choice here and you can study them first. No, they are not open source either.
@ChPech was it just kevlar fiber alone? You have to have something extruded to embed it in, normally nylon. That’s the reason for a dual extruder machine, but the second extruder isn’t the typical extruder we use
@brian_alley I extruded petg and tried to inject the fiber after the extruder using a 1.2mm nozzle, like this: http://www.nature.com/articles/srep23058