Their main chart is called Melon Top 100 and its rankings are essentially based on:

Unique listeners from the last hour and from the last 24 hours.

60% downloads and 40% streams for each unique listener.

This chart updates every hour. From 1AM to 7AM, a chart freezing policy applies and data from the last hour is no longer taken into account. This system is exactly how their previous chart Melon 24 Hits worked, so people usually refer to the chart by that name during those freezing hours.

There's also an "unofficial" chart called Melon Real Time that is actually just the old chart that Melon used until Mid-2020. This chart also updates every hour and freezes from 1AM to 7AM, but it only considers data from the past hour. It technically doesn't exist anymore, but Melon still provides unofficial ways to access that chart.

Melon also has daily, weekly, monthly and yearly charts. They are simply an aggregation of the cumulative unique listeners that each song had for that time-frame.

And finally, Melon introduced a new chart in 2023 called Melon Hot 100 which works essentially in the same way the old Melon Real Time worked but considers only the latest releases. This chart has two different time-frames for releases: 30 days and 100 days.

YouTube Music has two charts, which are updated on a weekly basis:

Top Songs

Top Music Videos

The criteria is super straightforward, the song with the most streams gets a higher ranking. For Top Songs, every stream of the song is counted (including fan cams, live performances...) while for Top Music Videos only streams of the official MV are counted. Both charts are updated every Sunday morning, with no specified hour. The tracking period goes from Friday to Thursday.

There's only one chart that updates every hour based on data from the past 24 hours and it only counts streams (no downloads), but their data is not transparent so you can't see the actual number of streams each song gets. Since this chart takes data from the past 24 hours into account, new songs usually take a few hours to enter it.

It only has a real time chart that updates every hour and it's based on 50% downloads and 50% streams. The freezing policy also applies to this chart from 1AM to 7AM. And while every other chart is a Top 100, Genie is actually a Top 200.

It also has daily, weekly, monthly and yearly charts which also use the same criteria for their rankings. Finally, Genie also provides a number of total unique listeners and streams for each song though it doesn't seem to use it for charting purposes.

Bugs has a real time chart that uses 80% downloads and 20% streams as criteria, also applying a freezing policy from 1AM to 7AM. Because downloads have a bigger weight, new songs usually get a boost in this chart. It also doesn't have transparent data for the amount of downloads and streams. On top of the real time chart, there are also daily and weekly charts that operate using the same criteria.

Vibe only has a daily chart that updates at 7AM KST and it's based on unique listeners too (they call it "1 stream per 1 ID policy"). Much like FLO, its data is not transparent so it's not possible to see the actual number of unique listeners of each song.