Picnik is a browser-based photo editor. It feels similar to a desktop application with top and side navigation, and instant previews of any effects or edits. Picnik can grab photos from your hard drive, or online photo hosts and social networks. It can also export any edited photos back out to these sites, letting you make changes to large files without having to download, then re-upload.
Picnik has two levels of service, both a free and premium one. The premium service removes ads from the site, and adds extra effects filters, fonts, and features that eventually trickle down to free users.