Webmakers/Tools
StencylWorks - mobile game builder (built off Scratch technology) http://www.stencyl.com/
DEFCON Kids (Las Vegas, July 28-29) - "dedicated to teaching kids around the world how to love being a white-hat hacker. A white-hat hacker is someone who enjoys thinking of innovative new ways to make, break and use anything to create a better world." http://www.defconkids.org/
HacKid Conferences (Atlanta, March 17-18, San Jose TBD) "conference focused on providing an interactive, hands-on experience for the entire family — kids aged 5-17 & their parents — in order to raise awareness, excitement and understanding of technology, gaming, mathematics, safety, privacy, networking, security and engineering and their impact on society and culture." http://www.atl.hackid.org/
Game Closure Game Closure makes a javascript multiplayer SDK for both mobile and web clients.
AppMobi AppMobi makes HTML5 development tools of miscellaneous nature for mobile and web clients.
CocoonJS by Ludei (Ideateca) Ludei makes a SDK for javascript games and supports web (openly) and mobile (by license)
Spaceport.io (sibblingz) Spaceport is a SDK for developing flash like html5 games on mobile.
Adobe Adobe makes Edge and Wallaby export to HTML5 tools.
GameSalad GameSalad makes drag and drop game creation tools so that non-programmers can make interesting mobile games, and in some cases, HTML5 too.
Scirra Construct2 - Drag and HTML5 game creator
ImpactJS ImpactJS is a one man engine for making HTML5 platformers. Scenegraph style.
Appcelerator Titanium This is an end to end toolsuite that can build all sorts of applications.
Google Swifty converts content from Flash to HTML5