BetterFps is a Minecraft mod that add a few performance improvements, trying to be compatible with other mods.
All improvements can be enable or disabled in the config file (config/betterfps.json) or in the options menu (Options -> BetterFps Options) (For older versions, press F12 while in game).
Algorithm
Changes sin() and cos() algorithm. There are 7 algorithms. Each one of them may or may not help you, it really depends on the hardware of your computer.
Currently, it's pretty similar from what FpsPlus used to do, but it doesn't edit base classes.
I have plans to expand this, not in more algorithms, but in algorithm generation based on benchmarks.
Affects both client-side and server-side.
Memory Preallocation
Removes a RAM preallocation of 10MB. This allocation was added to prevent players from starting the game with low memory, but this allocation is kept until its almost the memory reaching its limit. This was made just for players using modpacks, where memory might be a problem. If you have enough memory, this is pretty much useless for you.
Only affects client-side.
Fog
Removes the fog. The fog creates a lot of lag, why not add an option to remove it?
Only affects client-side.
Beacon Beam
Removes the transparent layer of the beam. It might help it when there's a lot of beacons.
Experimental - I'm still testing if it actually helps anyone, I might remove it.
Only affects client-side.
Fast Hopper
Hoppers are very unoptimized, they keep checking for items to pickup when there's no need for it. Simply putting a solid full block on top of it stops looking for items to pickup.
Recently, Forge has added the new capability API, which forced me to remove others improvements. I might reimplement them in the future.
Only affects server-side.
Fast Beacon
Beacons are also unoptimized, the code processes stuff that it didn't need to. Not only it was recoded thinking in performance, the code was also organized for processing stuff only when it needs to.