In addition to the many commonly known egg substitutes, there is one less known: aquafaba.

Aquafaba is the resulting liquid from cooking beans and other legumes such as chickpeas in water, and it is quite useful as a substitute for eggs. The official aquafaba site (http://www.aquafaba.com) explains the history, the science, and  what has been said about aquafaba.

There are cook books devoted to the use of aquafaba in recipes from lemon cake to Pavlovas and Swiss buttercream: 
https://www.amazon.com/gp/product/1612437214/ref=crt_ewc_title_oth_6?ie=UTF8&psc=1&smid=ATVPDKIKX0DER