I found Amazing Adventures 5e when I wanted to run a Pulp Adventures campaign, inspired by the old polyhedron magazine versions of Pulp Heroes (both D&D 3.5 and d20 modern hacks). This is an all-in-one-solution--you don't need any 5e books to play, just this one.
It supports adventures anywhere from turn-of-the-century to sci-fi and I've used it as the platform for my streamed Actual Play campaign that bends genres. That game's been running for over a year now. Many of the classes are recognizable (Pugilist is the Monk with some changes and different flavor text), some have been overhauled (the Hooligan is the Rogue but with more changes, and the Socialite isn't a bard but has several things in common), and some are unique to this ruleset (the Gadgeteer and the Mentalist).
Aside from modern/pulp/futuristic equipment and vehicles (and the rules for running them), the book also includes a more realistic/simulationist set of rules for firearms that are more deadly and exacting, which will be a welcome plus for any fans of more sophisticated mechanics.
I've greatly enjoyed this book, importing other 5e material into it is not difficult, and it is all you need to run amazing 5e adventures for any modern time period.