ImageJ - For Mac and PC - an image processing and analysis application written in Java, widely used in the life sciences fields, with an extensible plugin infrastructure.
Loci Tools - ImageJ plugin for opening Nikon C1si Confocal files as well as other formats in ImageJ. To Install, place the .jar file into the plugins folder located within the ImageJ folder.
Nikon EZ-C1 Freeviewer - Windows 7/Vista/XP app for viewing and performing simple tasks with Nikon C1si Confocal files. To install, unzip files, and run installer application.