Photivo is a free and open-source (GPL3) photo processor. It handles your RAW files and your bitmap files (TIFF, JPEG, BMP, PNG, and many more) in a non-destructive 16-bit processing pipe with gimp workflow integration batch mode.

Photivo tries to provide the best algorithms available, even if this implies some redundancy. So, to my knowledge, it offers the most flexible and powerful denoise, sharpens, and local contrast (fake HDR) algorithms in the open-source world.

Features

16-bit internal processing, color managed with LCMS2.
Gimp workflow integration (import and export)
Works with RAWs and Bitmaps (8 bit bitmaps are transformed and processed with 16 bit, which usually gives better results).
CA correction, Green equilibration, line denoise, badpixel reduction, wavelet denoise, median filters on RAW data.
Perspective correction (tilt and turn), distorsion and geometry (also defish) correction
Demosaicing: Bilinear, VNG, VNG4, PPG, AHD, DCB, mod. AHD, VCD, LMMSE, AMaZE (needs work!).
RGB, R, G, B, L*, a*, b*, Texture, Detail, Denoise, Hue, Saturation, L* by Hue, Base curve.
Tone mapping (Reinhard 05 (RGB Brighten), Fattal et al. (Dynamic range compress)).
Several local contrast filters (HiRaLoAm (Local contrast), texture contrast, local contrast stretch).
Sharpen (Edge avoiding wavlets, USM, Highpass, Inverse diffusion, Wiener filter, Gradient sharpen).
Denoise, seperately on Luminance and Color (Edge avoiding wavelets, GreyCStoration, Wavelet, Masked bilateral, Pyramid) and via a hue or luminance sensitive denoise curve.
Adaptive saturation.
Film grain simulation.
Black and white conversion.
(Split) Toning.
Cross processing.
Gradual overlay (like Cokin(R) GND filters).
Vignetting.
Softglow / Orton.
Texture overlay (external texture)
Fake tilt/shift, toy effect
Batch mode
Translations: Dutch, French, German, Italian and Russian.