Pretty much every Mac fanboy knows and likes
Skitch. Me too, although I seldom use Mac.
There is however one major (OK, more than one to be honest ;)) problem with Skitch. It's only for Mac OSX and there is no sight of so desired Windows support. In fact
the original blog post at Skitch website (dated March 2008) about it has been mysteriously removed - here is
the cached version by Google. Not to mention Linux. Another drawback is that you cannot easily access Skitch from anywhere. You have to install it first. Inconvenient.
ScreenSnipe comes to the rescue.

When I completely switched my development environment to Linux, I missed so much a screenshotting tool which would be as simple and beautiful as Skitch. Gimp made me mad (sure, after years I've finally mastered it, but initially, to draw one stupid arrow and a text, I almost cut myself). Thus I decided to write my own screenshot app. That's how ScreenSnipe was born.
I wanted to go one step further – make it really cross-platform and installation-less. A screenshotting tool for the 21st century and Web 2.0 era.
I think I am getting there. ScreenSnipe is maybe not so snappy (yet) as Skitch, but it has some completely unique features, it evolves quite fast and is really installation-less (directly available from the web browser) for all these 100-million or so PC users who happen to have Java 6 installed on their boxes. It runs on Windows, Mac OSX and Linux (and maybe on other systems which I have not had a chance to test).

A couple of months ago I released a fully integrated
ScreenSnipe with Atlassian JIRA – my beloved issue tracker. Last weekend I released something which I desired even more – simple yet powerful and collaborative (editable) screenshots directly in Atlassian Confluence – a wiki (or perhaps I should say a collaboration platform) which I love and use every day.
ScreenSnipe for Confluence makes an annotated screenshot a first class citizen of this enterprise collaboration system. Not only you can easily make screenshot and annotate it in many ways, disguise, emphasise, crop, zoom. You can publish your screenshot with a single click in Confluence page (or blog, or comment) and this picture will be editable (as vector graphics) for every person who can modify attachments of this page. You can easily just replace the underlying screenshot, leaving the annotations intact or just slightly modified to match new graphics.
Think about technical documentation (and pictures often not catching up with the evolving UI), release notes, visual discussions, UI and UX reviews, QA. All of these is now hopefully much simpler and more effective.

ScreenSnipe for Confluence (as well as SS for JIRA) comes with a completely free
30-day trial. Installation on the server side is really simple (just upload a single jar file). No need to do anything on the client side.
Enjoy.
P.S. To celebrate the release, ScreenSnipe for Confluence is currently offered with 20% discount.