Extentech has released today a MindTouch Sheetster Add On which means MindTouch users can now edit Excel spreadsheets inline without leaving their environment, all for no extra charge. Here is a quick Video demo of the feature (turn the volume down if you don't want the annoying music track).

Sheetster is entirely open-source based where anyone can build a standalone Java app server that serves up dynamic spreadsheets.. This is another alternative to the raft of online spreadsheet data-sharing tools that I reviewed last week.