Be-Boy Kidnapp'n Idol

Gravitation and Be-Boy are all about music and shounen-ai, the first gives an almost equal weight to both themes while the second is more concerned with romantic nuances. With this said, Gravitation is essentially a comedy with its angsty moments while Be-Boy is more serious albeit not as well accomplished. Fans of one should probably be interested in the other.  

Kind of the same type atmostphere and corprate feeling 

The two protagonists of these '80s OVAs have a similar relationship with one another, and both shows feature a plot with an evil talent agency/record company. Also, the more "innocent" main character is voiced by the same person. 

Lesson XX and Be-Boy tell a similar shounen-ai centred story in which two male leads go through the first awkward stages as their relationship goes from friendship to romantic. They have the same look in terms of artwork and the mood is somewhat akin, however, Lesson XX is considerably more realistic and goes in depth regarding character development while Be-Boy has a contrived plot that feels somewhat rushed.  

Sukisho and Be-Boy are shounen-ai productions that play on the mains misunderstanding each other. Sukisho is mostly a comedy but has a very dark backdrop while Be-Boy is cute and mostly harmless. In both the relationship between the boys is tested and it is likely that these anime share the same fanbase.  

A music setting, shounen-ai and plenty of angst dominate Be-Boy and Zetsuai. In both we have a romantic relationship between a singer and a person not involved in the music business. Be-Boy is more light hearted, though, and has plenty of fluff while Zetsuai is virtually charged with extreme angst, dark pasts and plenty of emotional suffering.  

Seikimatsu Darling and Be-Boy both take a shot at creating a cute shounen-ai romance story. The first succeeds considerably better, adding plenty of comedy and cleverly undercutting some of the conventions of the genre while the first relies more on angst and improbable plot gimmicks, yet there is an affinity in both titles and enough to assure that fans of one should find something of interest in the other.