Orbital Frontier
Download it.
It is early, it is free, and it changes most days. The build below is the newest one that finished building; your space program lives on the shared world, so it follows you between this and your phone.
macOS
“Central Finite Curve: Flight Beside Another Player”
Download orbital-frontier-0.228.1-41.dmg
Needs macOS 11 Big Sur or newer.
Signed and notarized by Apple. Open the disk image, drag Orbital Frontier into Applications, and double-click it.
Earlier builds: 0.227.1 (40), 0.204.1 (35), 0.202.0 (34), 0.195.1 (33)
SHA-256 6abe527a20a48f6ad37a24e7d682bf75852d9e61f1be33db7107164cfd0c5d63
On a phone
iPhone and iPad go through TestFlight, and Android is installed from a file or from Play once there is a listing. The front page has both, and the manual says what signing in carries between them.