Special record label collaboration project releases

Now here's something that hasn't been brought up as much in this site as it really should; special collaboration projects by record labels, featuring various bands and their members. Impressive projects like this are very rare nowadays, but checking out the ones that exist are a great way to explore material made by different members of different bands, often altogether, and even get interested in some of those bands. Any musicians from at least one metal band you love and enjoy? Those albums have it all! Here's perhaps the most famous example:

Roadrunner Records is one of the most famous and diverse metal/hard rock record labels of all time. Famous and infamous bands signed to the label like Slipknot, Trivium, Fear Factory, and Machine Head have made the label as big as it is. And the then-core members of each of those 4 bands were chosen for ambitious project conceived by ex-vice president of the label Monte Conner. He wanted to do a special thing for Roadrunner's 25th anniversary. He wanted 4 members of different bands band together to make an album dedicated to the label. But then he decided to upgrade his idea into something more ambitious... The 4 chosen ones, ex-Slipknot drummer Joey Jordison (RIP), Trivium frontman Matt Heafy, Fear Factory guitarist Dino Cazares, and Machine Head frontman Robb Flynn were tasked in each recording 4 songs (though one captain would have a bonus 5th) and choose any member of a Roadrunner-signed band past or present to record with them. The end result is a massive 18-song 77-minute album featuring 57 artists from 45 bands! Here's to another impressive project like this in the future, hopefully in Roadrunner's 50th year, 2030. Anyway, this release is currently tagged as alt-metal, but you can't deny the metalcore, thrash, groove, and to a lesser extent, death/black metal appearing here. Here's my genre analysis for the 14 tracks of the album:

1. The Dagger - thrash metal/groove metal/metalcore

2. The Enemy - death metal/thrash metal/metalcore

3. Annihilation by the Hands of God - death metal

4. In the Fire - heavy metal/speed metal

5. The End - hard rock/alternative metal

6. Tired 'n Lonely - blues rock/hard rock

7. Independent (Voice of the Voiceless) - thrash metal/groove metal

8. Dawn of a Golden Age - black metal

9. The Rich Man - nu metal/alternative metal

10. No Way Out - alternative rock/pop rock

11. Baptized in the Redemption - groove metal/nu metal

12. Roads - acoustic ballad

13. Blood & Flames - groove metal/sludge metal/metalcore

14. Constitution Down - groove metal/thrash metal

15. I Don't Wanna Be (A Superhero) - hardcore punk

16. Army of the Sun - heavy metal/alternative metal

17. No Mas Control - groove metal/nu metal/metalcore

18. Enemy of the State - gothic metal/doom metal

Primary genres: Alternative metal, groove metal

Secondary genres: Thrash metal, metalcore

The alternative metal tag will still be kept on for this album as a general genre for many of the songs covering alt-metal, nu metal, and alt-rock, but it's as dominant as groove metal there. I'll make a judgement submission for this album soon. Anyway, does anyone here know any special releases similar to this, with dozens of members from different bands in the same record label for a special occasion? Discuss!