Captain Squeegee. A rare combination of ska and psychedelic rock. Their album To the Bardos! is particularly great, and ranks among my top 5 albums of all time.
Black Bonzo. A modern-ish prog band that sounds straight from the 70s.
Bubblemath. Progressive jazz fusion. Their first album was light on the jazz and pretty low-budget, but their second album, Edit Peptide, is the best in the subgenre, IMO.
Lotus Child. Indie alterna-rock. They only had one album, but it's creative and interesting.
He's excellent. If you like industrial metal or the Doom soundtrack you'll probably like ToD. There's no vocals, so I imagine this will appeal to DnB and EDM fans as well.
I recommend Generation Bliss (link for bandcamp because it's not on Spotify.. wtf bro this your best album!)
Monarch ! the slowest band on earth a French Drone metal band who is heavy as hell and plays so slowly that it's edge between music and noise. Pretty great if you want to set-up a dark-ambience or want to chill out over slow music.
Also they're great on stage and the musicians are accessible like you can talk with them after the concert
Technically they're just over the 5000 monthly listeners limit (6955), but Xanthochroid is still relatively unknown and my favorite band of all time, so I can't not share them.
Future Unlimited. I'm not sure if they still make music, but I love pretty much all their songs. Their most popular upload has just 40k views. They are just criminally underrated in my opinion, I always hoped they'd make it big.
Argyle Park and their official unoffical sequel AP2. Around 2.5k combined. My favorite song is "A New Wound" which is actually incorrectly listed as "A New World" but it is so unpopular that will probably never be fixed.
Found them through their singer's YT channel. They describe themselves as acoustic stoner rock, which I feel is a good description. Lots of influence from Queens of the Stone Age.
Technically they somehow exploded to 5800 monthly listeners, but Valkyrik could use some more love. Last time I checked all their songs were at >1000 plays, even though, again, that somehow changed recently.