First of all, yes, 3 planets doesn’t count as a “planet”, singular, I know, but it sounds better this way… Whatever, on to the topic.
While this is not the first time, it is pretty cool that three planets have been found in an open cluster. This one is called the Messier 67. Open clusters are group of stars numbering in the thousands that are born from the same gas cloud. So for example, Orion Nebula may one day be an open cluster! Anyways, these open clusters eventually dissipate and the stars go on on their own. As for why this is important is the fact that crowded open clusters are believed to be planet unfriendly. That doesn’t mean it is impossible, but it does mean that finding some make them quiet special and fascinating to study at.
All three planets are gas giants. They were found by measuring the wobble of the parent star with the Doppler Shift. While we may not exactly know their size, we know their mass. They are 0.34, 0.40, and 1.54 times the mass of Jupiter. Let me remind you, of course, that all scientific measurements have uncertainties, and the one for the third one is particularly large, plus/minus 0.24. Interestingly, two of them orbit around sun like stars, although slightly less luminous than the sun (sun has luminosity 2, these two stars have luminosity 5). The planets themselves, though, orbit too close. They are the hot Jupiter varieties, and there is nothing like them in the Solar System. That similarity and contrast is what makes those planets very interesting. The planet more massive than Jupiter, on the other hand, orbit a giant star, but farther away. This one has what one might say a more reasonable orbit.
Other than that, there is not much more to say. They happen to be pretty cool because they were found in tight open clusters. You can look at the study, if you want all the nitty gritty details. You can also get a good summary from Universe Today here.