So I'm working on a sci-fi RPG that I'd like to run on the Saga Machine rules, but I'm not very good at legalese and I have some questions about the terms of the OGL. I need to know what I can use, what I can't use, and what I'm allowed to modify or change. I also want to know if the optional d10 mechanic is covered under the OGL. Can someone help?

No problem. Here's what you can use from Shadows Over Sol:

All of the game rules in the Saga Machine chapter, the Gear chapter, the Consequences appendix and the Dice appendix are available for use. The character creation rules in the Characters chapter are also open for use, as are all the stat blocks in the Non-Player Characters chapter.

The one exception to all of the above is that trademarks and art assets are specifically protected. That means you can't name your product “Shadows Over Sol” or “Saga Machine.” You also cannot reuse the art in those chapters and claim its use under the OGL.

Additionally, to meet the legal obligations of the OGL you need to: Include a copy of the OGL license in your product (most people cram it into a page of legalese somewhere in the back of the book). On that page you need to give credit to any OGL sources you're using in your product (in this case you'd include a line stating that content is used from “Shadows Over Sol. Copyright 2009-2015, Tab Creations LLC.”).

That's it for OGL requirements. However, if you want to use the Powered by Saga Machine logo (which is technically a separate license, since the OGL explicitly doesn't cover trademarks), you need to include the following line somewhere in your book: “Saga Machine™ is a trademark of Tab Creations, LLC. The Powered by Saga Machine logo is © Tab Creations, LLC and is used with permission.” (Typically these sort of disclaimers are put with the copyright notice somewhere near the title page.)

Thank you so much for the reply. Another question: what am I allowed to modify? Say for instance, if I wanted to change the wealth or initiative rules to a mechanic of my own devising, would the OGL allow me to do that?

evil_tendencies
Thank you so much for the reply. Another question: what am I allowed to modify? Say for instance, if I wanted to change the wealth or initiative rules to a mechanic of my own devising, would the OGL allow me to do that?

Yep. The OGL allows you to modify anything you can use.