An attractive English plum, sometimes known as Early Rivers, or, mistakenly, as a "river plum". Rivers' Early Prolific is, as the name suggests, an early and heavy-cropping plum. Rated by the Victorian fruit enthusiast Hogg as "a great bearer, and very hardy, rarely ever missing a crop".
It is dual-purpose, but arguably better for culinary purposes. (For dessert purposes, Opal is probably better).
Rivers' Early Prolific is easy to grow and crops reliably.