GTKRawGallery is an open source digital photo manager with an extensive list of powerful features.
This starts with a capable photo manager. A thumbnail browser supports several layouts to help you navigate your image library, for instance. You can organise your photos into custom libraries. And there are search tools, a tag editor, batch file renamer and more.
A Dcraw panel provides a host of RAW image processing options. You can tweak white balance, gamma, black point, saturation, brightness and more. There are denoise and media filters, along with a chromatic aberration tool and colour management options. You can save your preferred settings as presets, too, making it easier to reapply them consistently on future images.
If this is a little too complicated for you, though, the Transform tab has more straightforward tools: flip, rotate, resize and crop, red eye removal and so on.
A fairly standard (although well implemented) list of effects ranges from the practical (sharpen, unsharp mask, reduce noise) to the more artistic (oil paint, charcoal, sketch). All of these can be configured in various ways to customise the results.
And when you're happy, any selected images can be burned to disc, emailed, or uploaded to Facebook, Flickr, Picasa or Facebook.