Umihara Kawase is a momentum-/physics-based grappling hook platformer. Tight movement, non-linear level design, branching level progression. Don't mind the cutesy graphics, game's fuckin' tough.
First one is the hardest to complete once, second is the hardest to complete 100%, third is much more lenient. They all have slightly different movement.
All three games are on Steam - with additional practice modes, and without the temptation to savescum that an emulator would offer. Note that the games are virtually unknown and thus pretty hard to spot on sale.
There's also a fourth one in development, only announced for Switch at the moment.
N is a series of originally Flash-based games. Think SuperMeatboy, except more deliberate and with better level design. Momentum-based, with walljumps and other advanced movement tricks. Very readable minimalist graphics. Consistent movement across all versions (that I've played).
The first one (v1.4) still has my favorite set of levels, but I'm probably biased. The downside is that its framerate isn't as smooth as in the other ones.
Free on the dev's website.
Version 2.0 is also free and can be played
in a browser. Haven't replayed it in a while, but I remember disliking a lot of levels for either forcing a single path on you or for lazy enemy spam.
N+ is console-exclusive, never played it. The only one with online multiplayer.
N++ is the newest/last one. Steam-exclusive on PC, sadly no DRM-free option. Boasts a massive number of levels (4k+) - and that's not including the unintrusive implementation of optional challenges, which effectively more than doubles that number. Has additional fluff like soundtrack and color schemes.
..
After playing these, I can't help feeling that most other platformers are stuck in the stone age. It's the same rigid formula, you jump 3 tiles high, the platform is at 4, so you gotta jump on another platform first, rinse, repeat. Add enemies to hide the fact that the basic gameplay loop is braindead. Add variable jump height, dash, attack moves etc etc - in the end it's still fundamentally boring and can't compare to fluid freestyle momentum-based movement.
So, is there anything else like this out there?
(don't say Warframe)