Esperanto from German
I just came across this resource, and thought I'd pass it on.
Lingolia website is available in English, French, German, Spanish and Italian (depending on which of the target languages you want to learn). For example, Esperanto is currently available from German.
The languages offered are English, Esperanto, French, German and Spanish.
I did some grammar checking, and found their examples to be very clear.
Lingolia: einfach besser in Sprachen https://www.lingolia.com/de/
Each language covers topics easily found in a left sidebar, such as: -- Grammatik / grammar
-- Wortschatz / vocabulary
-- Schreibschule / writing school
-- Hilfe / glossary, dictionary, etc.
(-- Landeskunde / regional studies)
The Esperanto from German section offers a German-language book (12 euros) Esperanto – einfach, kompakt und übersichtlich / Autor: Heike Pahlow / ISBN: 978-3-96008-386-3 / Umfang: 144 Seiten, DIN A5 / Engelsdorfer Verlag, Leipzig / Preis: 12,00 € (D) /
The Esperanto section Eo-from-German website also lists Esperanto courses and events happening.
It looks like the site is still building (some pages, like the Landeskunde for French) may be in development or not available yet, but it seems promising.