Pixlr.com (Editor and Express) (right click extension)
Photopea - Saves in .PSD format and edits existing .PSD files
Lunapic (right click extension)
Picozu (Chrome App)
Ribbet (Chrome App) - Access Google Photos and save back in Google Photos
Mecabricks - Online Lego builder that can be downloaded for 3D printing. No registration needed to build but user must be logged in to download files and save.
Planner 5D - Interior design site
Roomstyler 3D - Room planning site
Tinkercad - Great 3D design site. Does require log-in.
Beautiful Audio Editor - Chrome-based audio mixer
Mix the Cloud - DJ crossfader for Soundcloud and YouTube audio
Soundtrap - Multiple layer audio mixer
Speak Pipe - Receive audio messages or use as a super simple audio recorder
Google CS First: Create your own Google Logo | More information
Scratch - MIT's open-source programming platform
Book Creator App - This one does require some front-loaded setup but is a great tool for students to share learning. Book Creator Ambassador Kelly Croy shares some insight on this episode of this Wired Educator podcast.
Adobe Spark - All kinds of creativity tools.
Screencastify - Record your screen WeVideo - Video editor
Photofunia - Small number of image effects may contain weapons or be of a PG nature.