I'm looking for something sort of like parent settrack so that I can advance players to a specific group on a track. However, I don't want it to blindly set their rank because some players will already have a higher one.

Thanks.

Check this and this

Example usecase?

That sounds like a good excuse to have several ladders.
One for voting, one for donating and one for playing.

I had essentially the same idea, but I wouldn't have bothered creating a track for each achievement type because the track would only have a single group. That idea would mean creating a group for each achievement. However, the achievement groups would only have a single permission to inherit the correct rank anyway. Instead of having players inherit a voter group that in turn inherits member+ and a playtime group that inherits member, I may as well flatten that to just inheriting both member and member+. In other words, I'd just be using parent add with the current groups. I don't like that for the same reasons as the people who suggested parent settrack.

You can use the scoreboard system. It can track everything you see in the achievements list, then figure out how to run a command when the score for a certain task reaches a specified number.

If you must use a plugin, here is one for spigot and bukkit, or here is one if you're on sponge

It would work nicely with automatic rank ups from various achievements. Specifically, we use AutoRank to advance players to a member rank after they've played for a few hours. However, that player may have already achieved a higher rank by voting, donating, or whatever other reason. The same thing happens if a donor starts voting and reaches the required number of votes for a rank up. With a simple set command, they lose their rank.