Here are the list of festivals I recorded earlier, and there are room for more!
August – Lughnasadh, Opalia, Vertumnalia, Nemoralia, Portunalia, Vinalia Rustica, Consualia, Vulcanalia, Opiconsivia, Volturnalia
Of those, I can see some thematic similarities, which probably have to do with the harvest and with the agricultural cycle in general in any case. I find it interesting that we seem to have protectors of cattle, fire festivals, and deities having to do with plants and agriculture, earth and fertility, overlapping. This is relatively stream of consciousness on my part here - and I'd be really pleased to have a discussion with others on these topics.