Skitch is an oddball. For a start, the interface doesn't resemble any other Mac app. However, for grabbing content, annotating it and then sharing or saving it, Skitch really does the business.
You can capture images from your Mac's camera, drag it over to Skitch, or take a grab of the entire screen or a selection. However, content can only have the most basic of edits (crop and resize), but you can overlay all manner of annotations using Skitch's intuitive and non-destructive tools (which in themselves are also fine for composing quick, simple diagrams).
The final output can then be saved or copied to another application (using the 'drag me' tab, which is a great little innovation) or sent to your online Skitch account.
These features are all available in the free version of the application, but get dressed up for Skitch Plus and you get some extra bits and bobs, such as more editing tools (rotate and flip, watermarking, custom fonts, resize presets), an extra grab type (full-length web page, rendered to a flat image) and some other goodies.
However, note that the price-tag isn't a one-off purchase and you have to unlock Skitch Plus annually.
Given that Skitch has survived online through a lengthy beta run, its longevity seems assured, although it's perhaps less robust in that regard than Flickr.
However, even if you never use the online component, Skitch is definitely worth downloading as an alternate means of grabbing content, making quick notes and sharing the result with your friends and colleagues.
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