CaptainOrs
Mongoose
Bundle of Holding has a MegaTraveller bundle right now for people who want some of the old source material or adventures. It will run another 18 hours or so. I haven't read the MegaTraveller books in years, but I imagine it wouldn't be hard to convert to Mongoose.
https://bundleofholding.com/presents/MegaTraveller
https://bundleofholding.com/presents/MegaTraveller