What is X3F, and why this page?
X3F is a file format for Sigma cameras, containing Foveon based images. I assume, as you are here, that this makes perfectly sense to you :)
The reason for this page is that I (Roland) am interested in the Foveon technology and that I have written some software to read X3F files. It all started by me reading news in rec.photo.digital in 2001 or so. And then later reading the Sigma SLR forum at DPReview.
Open Source and Kalpanika
The code gave evolved and can now also generate color images. This is mainly due to some work made in the Kalpanika company. For some time, the development was internal to the company, but now it has become open source again. You can find it all here Github.
To download the latest release, you can take a look here. Releases. Please do download the latest release. There are several versions build for each release for Linux, OSX and Windows. In the release you will find a README file that describes how to use the code.