I am currently working on the Soviet UR-700, Still a way to go, particularly with the upper sections. This was the alternative to the N-1 in the Moon Race, and it was a monster. It’s built around a cluster of 9 rockets, based on the UR-500 which appeared as the Proton. The outer 6 are over fuelled, and transfer the excess to the core 3 as they go, so that when they are dropped, the core 3 are fully fuelled. Above that is another Proton, (this with 3 engines instead of 6), and above that the LK-700 lander. Which is a bit like a big Apollo, with 3 extra service modules strapped to it. It was powerful enough for a direct ascent mission, which was seen as much less risky that the docking required for Lunar Orbit Rendezvous. The engines were developed and tested, the lander was built as a full size mock-up, and as each of the clustered rockets is based on a Proton, those were clearly also well developed. A version with nuclear upper stages was proposed for Mars missions.