'La Ondo de Esperanto' is an electronic magazine in PDF format. There are four numbers per year plus an end-of-year supplement. The magazine consists of 100-120 pages per number, so about 500 pages with the supplement.
The contents consists of various articles. The editor is Aleksander Korĵenkov, a well-known author in the Esperanto world.
To see an example of the magazine, see
http://esperanto-ondo.ru/Ondo/Lo-304demo.pdf