Weebly -- cloud-based web site development and hostingplatform
Zoho Creator -- cloud-based development platform for database-driven web applications
HTML Editor -- interactive cloud-based HTML editor
WebStorm -- powerful and intelligent IDE for JavaScript, HTML, and CSS (free for registered students)
CollabEdit -- syntax-highighting text editor for multiple programming languages
PasteBin -- another interactive cloud-based HTML paste bin
Picasion  or WeGIF  or MakeAGIF  for creating animatedGIFs
DaButton -- cloud-based button making tool
AddThis+ -- Social Networking Gadgets and Buttons
Screenr -- create screen casts
Cloud IDEs, Pastebins, and Editors
Cloud 9 -- HTML, CSS, PHP, Ruby, and JavaScript Cloud IDE
JEdit -- Cross-Platform Editor for JavaScript, HMTL, CSS, PHP, and more

LucidChart -- cloud-based visual modeling tool similar to Visio; supports storyboarding, UML, and other IS diagrams

Excel Live -- cloud-based version of Microsoft Excel
Google Sheet -- cloud-based spreadsheet tool

Wikidot | Wikispaces | WetPaint

The above tools are all cloud-based and are accessible through any browser that supports Flash and/or Java. Be sure to test them on mobile and ChromeOS devices. Unless indicated otherwise, the tools are free or an educational license has been obtained through a grant. Access the tools through the above links to obtain the free licenses.