I've been asked several times, recently, about some kind of licensing for others to publish products compatible with B/X Essentials. Thus...
B/X Essentials Compatibility License and Logo
The full text of the license follows. Please get in touch if you want to use it and have any questions!
This license allows unaffiliated, third-party publishers to release products declared as compatible with and for use with B/X Essentials. The following terms apply:
1. Your product's title cannot include the name "B/X Essentials" or the acronym "BXE".
2. You must include the compatibility logo somewhere on your product's cover (front or back).
3. You may use any of the compatibility logos included in the zip file along with this license (the standard logo, the inverted logo, the greyscale logo, or the inverted greyscale logo), whichever suits the visual needs of your cover best.
4. You may, optionally, place a plain box behind the compatibility logo, for clarity.
5. The compatibility logo must not be displayed so as to form part of your product's title.
6. The compatibility logo must be displayed smaller in size than your product's title.
7. The compatibility logo may not be colourised, made transparent, or have its aspect ratio (width vs height) altered.
8. Your product may not use the B/X Essentials trade dress.
9. You must not in any way state or imply that your product is an official B/X Essentials release.
10. Your product's legal text must contain the following: "B/X Essentials is a trademark of Gavin Norman. The trademark and compatibility logo are used with permission of Necrotic Gnome Productions, under license."
11. You must make an effort to ensure that all rules mechanics used in your product are compatible with the Basic / Expert rules, as presented in the B/X Essentials series.
12. You agree to take legal responsibility for your product, including copyright or trademark infringement claims.
13. Use of the license is free of charge.
14. After publication, you must provide a copy (PDF or print) of your product to Necrotic Gnome Productions.