This project has .NET and Java libraries for writing CZML content for use with Cesium. For a python library, see czml by @cleder.
See the CZML specification for more information on the structure of CZML.
Apache 2.0. czml-writer is free for both commercial and non-commercial use.
Binary releases are available on NuGet.
Binary releases are available for download on the releases page.
Check out the wiki, including the quick start and contributor's guide. Also browse the forum.