Online compiling of TikZ gallery examples
On each example page and also in the gallery views, you can see [TeX] and [PDF] buttons for downloading. Now there are new links: [Open in writeLaTeX]. Just a single click and you will land in the online editor which shows the code on the left side, and the output preview on the right side, automatically compiled in realtime.
For more information read the full article by Stefan Kottwitz.
Below is a screenshot of a TikZ example opened in writeLaTeX; underneath is the TeXample gallery with the [Open online] option on each thumbnail.