In this excerpt from the Agni Purana, Vishnu's horse-headed incarnation Hayagriva tells Brahma about how to install statues in temples. But he starts by saying this:
Listen to me speaking about the installation of (images) of Vishnu and others. (the principles) of Pancharatra and Saptaratra have (already) been described by me. They have been divided by the sages into twentyfive (books) in this world. Hayashirsha tantra is the first one. Trailokyamokhana, Vaibhava, Paushkara, Prahlada, Gargya, Galava, Naradiya, Sriprashna, Sandilya, Aishvara, spoken by Satya, Shaunaka, Vasishtha, Jnanasagara, Svayambhuva, Kapila, Tarkshya, Narayaniyaka, Atreya, Narasimha, Ananda, Aruna, Baudhayana, and the one spoken by Vishva as the quintessence of that (the prededing), having eight parts (or the other books).
For those who don't know, as I discuss in this answer the Pancharatra movement was one of the early movements that was important to the development of Vaishnavism. Its sacred texts consisted of detailed procedures to worship the sage Narayana, an ancient incarnation of Vishnu who was the twin brother of the sage Nara. (Nara and Narayana were the previous births of Nara and Narayana respectively.) Since the Pancharatra texts originated from Narayana himself, they're followed by pretty much all mainstream Vaishnavas.
But my question is, what are the "Saptaratra" texts that Hayagriva mentions, and what is their relation to Pancharatra?
As I discuss in this question, the name "Pancharatra" comes from the fact that the sage Narayana performed a five-day Yagna and as a result he "became everything". So are the Saptaratra texts a similar set of Vaishnava scriptures that originated with someone who performed a seven-day Yagna? There is a seven-day Yagna described in this chapter of the Taittirya Samhita of the Yajur Veda:
Kusurubinda Auddalaki desired, 'May I be rich in cattle.' He grasped this (rite) of seven nights, and sacrificed with it. Then indeed did be win all the domestic animals. He, who knowing thus sacrifices with (the rite) of seven nights, wins all domestic animals. (The rite) is of seven nights; the domesticated animals are seven, the wild seven, the metres seven, for winning both.
I discuss a related passage here, by the way. In any case, this web page suggests that Saptaratra was indeed a Vaishnava tradition akin to Pancharatra:
In addition to pa~ncharAtra the hayagrIva tantra remembers an independent tradition of tantric vaiShNavism termed saptarAtra, which was parallel to pA~ncharAtra, and contained the trailokyamohana viShNu tantra and hayagrIva tantra amongst others.
Hayashirsha (a synonym for Hayagriva) and Trailokyamohana are the first two texts mentioned in that Agni Purana quote, so that may be significant. Does anyone know where the Hayagriva Tantra mentions this? Are there any surviving Saptaratra texts?
I discuss some other non-Pancharatra Vaishnava Agamas in my question here, by the way.