I'm thinking of an idea to develop a widget lives within Gmail and do action on demand.
Like selecting a line of text clicking my button should create a task on a list (say asana.com)
I'm currently looking into https://developers.google.com/google-apps/gmail/contextual_gadgets
but wondering I'm heading right direction?
Check this one - http://www.streak.com/ they even have custom UI (in main view of gmail).
It would be really helpful if you share good resources and point the direction.
eg:
Gmail Contextual Gadgets (which work only in Google Apps Gmail, and not in "regular" @gmail.com Gmail) may not modify the Gmail UI - they are restricted to appearing in a rectangular area beneath a received message.
See www.wishery.com for an example.
To do the UI modification you illustrate, you must produce a browser extension - there are no native Google APIs to Gmail that'll help you (sadly!).