It depends on what you call a leveling system. if you mean just increase you capabilities then yes there are some. If you mean class-based go up a level kind then no because leveling up is inherently unrealistic, though E6 is close. If you take the second option, many skill-based systems would work though I only have significant experience with Cyberpunk 2020 and there system is when you use skills a lot you eventually get Improvement Points which you spend to increase your skills.