I started off using Adobe DNG Converter, but it precesses the files for you - they don't come out as a flat Raw-like files & they get smaller in size.
Have since moved to using RPP (Raw Photo Processor) & it has everything you need to convert them to many different flavours of TIFF or JPEG in a batch. You also get all the options to alter DNGs: Hot Pixel remover, WB, RGB&Luma, Exposure, Sharpness, 4 preset curves (Film-like, L, Gamma & Colorimetric Gamma), some really nice Film emulation presets & lots more.
If you want a proper free editing program (cause you don't have PS etc...), then some people have recommended using: Darktable & Raw Therapee
Have since moved to using RPP (Raw Photo Processor) & it has everything you need to convert them to many different flavours of TIFF or JPEG in a batch. You also get all the options to alter DNGs: Hot Pixel remover, WB, RGB&Luma, Exposure, Sharpness, 4 preset curves (Film-like, L, Gamma & Colorimetric Gamma), some really nice Film emulation presets & lots more.
If you want a proper free editing program (cause you don't have PS etc...), then some people have recommended using: Darktable & Raw Therapee