Here are some mens!
Here is a playlist: (these songs were taken from that "AllMathers" channel.)
I strongly recommend you to check John_Banana, a dope channel about leaked songs and you can find them in the highest quality, with artworks and some information as well.
Unofficial Slim Shady LP 2, this is made by fans and named "SSLP2", Eminem doesn't or didn't have a plan to do SSLP2 I believe.
Rock Bottom's Original Demo:
Bass boosted version: youtube.com/watch?v=FyRsibCdFcE
Relapse 2, contains leaked songs when Eminem was recording Relapse.
King Mathers, this album is actually pretty known back in 2007, Eminem wanted to quit rap at that time. The description says "A 2007 fan-made mixtape of leaked songs from Eminem's hiatus. During this time period, Eminem was struggling with depression & writers block, causing him to want to quit rap. This is the unreleased mixtape he was working on, but scrapped after he went to rehab."
G.O.A.T. from King Mathers:
Soul Intent mixtape: Contains "Fucking Backstabber", and "Biterphobia"
Soul Intent was a Detroit group, Eminem and Proof were in it.
DJ Butter Fingers (a DJ from Detroit) was in Soul Intent, he released some unknown Eminem's Soul Intent tracks.
Fan-made "Eminem - 2003" album, contains some known songs like "Hail Mary", "Can I Bitch", "Bully" as well.
D12 - Dumpin: A song came out after Eminem released Infinite.
There are many more on Youtube and Internet! For Proof (RIP!), sadly I don't know too much about Proof's underground/unreleased/demo music, but I'm pretty sure you can find some, and some of the links that I posted also contains Proof in some songs. Hope this helps! youtube.com/watch?v=HYeO0KSO9PI