Both have main riders based on the Japanese Rhinoceros Beetle. Both the protagonists are cheeky, Stronger in a more playful way while Kabuto is a very self confident rider. They are different as well as kabuto is the about super speed and stronger about electricity.

Both are the start of eras for Kamen rider with Kamen rider of course being the first ever rider and start of the Showa era while kuuga is the start of the heisei era

Both have main characters that make the world around them better. It feels like people's life's are improved by having met them. Both have iconography that invoke old civilization, while the ryusoulgers are part of the culture kuuga has to discover it's secrets by himself.

Both came out in the 90s while the show was off the air. They both look similar and fight multiple monsters over the course of the movie. ZO is leans more on sci-fi while J is more of a fantasy

Both feature villainous organizations where the higher ups constantly argue and one up eachother. In RX they do sever a leader while in jetman they are all trying to become the top dog

While RX is a lighter show it is still the direct sequel to black so if you want to see the next part of the story for our Kamen rider watch RX

Both have a darker overall plot but are very episodic with a lot of the episode plots being silly one offs. Lupat is sillier while black has a darker ending

Both have representatives from each previous Swanson come together and show the audience a bunch of clips

Both are series with a surface level space theme while changeman does more with having the go into space in the end while super-1 was training to be a astronaut before he became a cyborg

Super-1 is the sequel to skyrider both feature riders who are cool and level headed. Super-1 more unique thing with it's multi hands and focus on marshal arts but both end up as a basic Kamen rider series

Both are back to basics series with cool protagonists. Boonboomger has more interesting characters but that is because it is later but skyrider is still a good example of what these franchises are

These two have basically the same set up with a young man kidnapped by an evil organization that turn him into a cyborg to do evil with. Only to be freed by the one that upgrade then