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Cloud based IDE. What languages? Can't tell. It says it's for Ruby too.
Turn individual screen mockups into a flow. Very simple. Free.
DSL to draw graphs. Very good for showing off research or analytical results. Its easy to write a little ruby app which generates the input to graphviz
Interesting no-signup tool for shared editing
General database with synchronization accessible via javascript. seems very useful for mobile
Great set of online coding tools
Better Specs is a collection of best practices developers learned while testing apps that you can use to improve your coding skills, or simply for inspiration.
Ruby facts, opinions, source code, links, and stuff.