X3F2TIFF allows you to convert X3F files from SIGMA DP1 / DP1s / DP1x / DP2 / DP2s / DP2x cameras into TIFF. You need FlashAir or similar devices to download X3F files in Safari.
If the TIFF data after conversion is too dark, try changing the max value in the settings to 500 or 300. Please use iPhoto, Snapseed, or similar apps to edit the converted photo.
Only iPhone 4S is tested. It may / may not work on older devices with less memory.
The support is provided via Website or twitter(@unitkay).
Ratings and Reviews
Using the X3F2TIFF app and the Toshiba FlashAir card and its app, I was able to get tiff files into my iPhone 5 from my Sigma DP3M and edit them in Snapseed. Unfortunately, the files are too washed out & colorless for even Snapseed to make into a normal-looking image. While the app is of little use to me except as an experiment, I'm giving the app 2 stars for the technical achievement.
With Family Sharing set up, up to six family members can use this app.