Longshot Space, recently featured in the „First Principles“ podcast, wants to reduce cost to orbit by building a ground hypersonic pressure-based gun.
See:
https://open.spotify.com/episode/4vf0LkUTKz8RwPTkJcE2mW?si=6lsWMR_-R8ObAoixgQvmfw
And https://www.longshotspace.com/
Will they be successful? Meaning:
100 tons payload delivered to Low Earth Orbit by 2050.
Massive technical challenges, but also massive economic challenges. Even if they are (by some miracle) able to raise enough funding, solve every technical challenge, and build a working copy of the thing, they'll still only be able to deliver low-value payloads (bulk materials able to tolerate the Gs) to a single orbital plane. And they'll have strict limits on how large the payload can be, and (unusually) limits on minimum density for the payloads.
Yes, they'll be less energy intensive than Starship (by avoiding the rocket equation), and maybe they'll genuinely cheaper for it, but stacking the two reusable systems against each other, I think people will more than happily pay a premium for their payloads to have a gentler ride to the correct orbit.
Like SpinLaunch, I have to think this is, charitably, best thought of as a pathfinder for the tech. It may eventually have a useful role on the Moon or Mars, thanks to their lower gravities and relative lack of atmospheres. However, these companies are going to go broke.