Open source solutions for Landsat-8 mosaicing and correction?

You may consider GRASS GIS which offers a rather complete processing chain for Landsat including radiance correction for Landsat 8. For details, see

http://grasswiki.osgeo.org/wiki/LANDSAT

Examples:

• Landsat 1-5,7,8 data import
• Auto-enhance colors, natural color composites
• Calculate Top-of-Atmosphere Reflectance and band-6 Temperature
• Haze removal
• Atmospheric correction
• Cloud identification
• image classification
• time series analysis
• Export of results