We’ve had this request for years, and always conclued that licensing Rhino is the best option. People tend to start with “we just want a couple functions from your geometry library” and then throughout the conversation also mention that they’d like to be able to read and write all the file formats that Rhino supports, and also have “just a simple 3D display of the objects” to preview them, or maybe even be able to pick them. Pretty quickly, it turns into needing all of Rhino.
If you’re certain that you just need Rhino’s geometry computation, we’ve made Rhino.Compute available. It exposes all of Rhino’s geometry tools, as well as the ability to solve grasshopper and python scripts, as a web API.
The Rhino.Compute service runs on your infrastructure, and is billed per core per hour that it is running (rather than by one-time licensing fees). Please check it out and ask any questions that you have.