Where it came from
The first tagged release in the repository, v0.5, is dated 12 April 2020. The about page credits the work to one handle, "@craigraw", and the download page identifies the release signer as "Craig Raw [email protected]". Everyone else named on that page is listed under "Supporting", which is the donation list.
Structure, honestly
Sparrow names no company. The about page says only that it "is open source and will always be free to use" and asks for donations, and the documentation notes that "as an open source project Sparrow Wallet does not have a support team". No legal entity could be established from the project's own materials, and no statement was found that one does not exist. That is why this entry reads Undocumented rather than Unincorporated: not finding a company is not the same as there being none. The software is licensed under Apache 2.
What it built
Sparrow is a desktop application built around PSBT, the partially signed transaction format, which is what lets it act as the coordinating layer for hardware devices it did not make. The documentation lists Trezor, Ledger, BitBox02 and Jade over a cable; Passport, Jade, SeedSigner, Keystone and Krux over QR codes; Coldcard, Keystone and Passport over SD card; and Tapsigner, Satschip, Satochip and Keycard as smartcards.
It also assumes you may want to run your own node, and connects to Bitcoin Core directly rather than routing your addresses through someone else's server. Release binaries are reproducible from v1.5.0 onwards, and the build instructions are published so a third party can check them.
What it changed
Sparrow made the coin-level view normal on the desktop: which UTXOs you hold, where they came from, and what a transaction is about to reveal when you spend them together. It also became the neutral ground where devices from competing vendors work in the same wallet file, which is the practical benefit of everyone agreeing on PSBT and output descriptors. Listing here is not endorsement.