National Geographic's Open Explorer site is a digital field journal where explorers of the world (or just their backyard) create and go on expeditions and share their stories along the way.
826 Digital is aligned to the Common Core ELA standards but can also work for writing programs in states with their own standards.
Workbench is a PBL platform where students can complete STEAM tasks using everything from basic art supplies to technologies such as Sphero, Makey Makey, Raspberry Pi, and more.
Tinkercad is a free, kid-friendly online computer-aided design (CAD) program where users can design, modify, and print 3D objects.
The projects offer well-crafted tutorials, guides, and videos, which are tremendously easy to follow.