LogFAQs > #964536850

The Chicago series' have been mentioned, Arrowverse already mentioned (I will add they had Ezra Miller cameo as the DCEU Flash on the last major crossover which also had Tom Ellis cameo as Lucifer)

Grey's Anatomy and Station 13 have done some (at least one a season)

911 and 911: Lonestar have done at least one a season

The FBI's on CBS crossover all the time, CBS is big on cross promotion actually: The NCIS's cross over with each other but also bleed into Magnum PI (and MacGuyver and Hawaii 5-0 when they were on) I am personally waiting for the Magnum Blue Bloods crossover. (Blue Bloods has somehow managed to avoid doing any crossovers in the more then a decade it's been on tv)

Funny aside, Katrina Law joined 5-0 during it's final seasons and then after 5-0 was canned she got a part on the og NCIS as a different character despite the team knowing her in her 5-0 role.

The Law & Order's have been crossing over for years.

NBC has actually been doing a shared universe for their comedies recently: Cloud 9 shows up outside of Superstore, Payne Motors logos have been appearing on cars outside of American Auto. Not really a crossover per se, but neat easter eggs that could lead to crossover episodes.