Spline Editor 1.0 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus. The actual developer of the free program is Romain Guy. The most popular version of the program is 1.0. The software lies within Desktop Tools, more precisely Themes.
From the developer:
It lets you defined splines you can use for non linear interpolation in the framework. The editor actually uses the framework to play some effects.
Property ranges let you easily animate Swing components. For instance, you can ask the framework to change the background color of a JButton from blue to red over 400ms at 60fps. It's really great and better stuff are on their way.
You may want to check out more software, such as Magic Photo Editor, GIANTS Editor or Reezaa MP3 Tag Editor, which might be similar to Spline Editor.