These are just a few notes explaining the tier rankings and other considerations for psionic manifesters.

Dreamscarred Press published most of the material for manifesters in Pathfinder, but manifesters were first-party (published by Wizards of the Coast) in D&D 3.5.  These notes apply to traditional manifesters of psionic powers such as Psions, Wilders, and Psychic Warriors, as well as less conventional psionic-themed characters such as Soulknives, Aegis, or Dreads.

Generally, psionic powers are nearly as versatile as spells, and so characters that can manifest powers tend me be high tier.  Some options, such as the Spell-to-Power Erudite or psychic reformation, greatly expand the versatility of psionic manifesters.  There are also several known tricks to enable infinite combos - don't even think about it.  Psionic characters can also break the action economy if built right.  Manifesters that can double their actions per turn warrant a tier increase.

Ledge Campaigns use full magic/psionic transparency.  I'm open to changing this, but in that case I'd need to create more homebrew material to fill the gaps.  I'm also open to High Psionics, but this option probably warrants a tier increase for lower-tier classes, such as the Soulknife.

I'm aware that the Hyperconsciousness book is arguably in second-party territory (as it was written by many of the designers of D&D 3.5).  For now, the book will be considered third-party.

2023 Notes: I've decided to allow the High Psionics rules for manifesters.  We'll not be replacing the Wild Talent feat, but Aegii and Soulknives will benefit from "+1 level of existing manifesting class" prestige classes.  Soulknives have the gifted blade archetype in addition to their normal features (so they retain their psychic strike, etc.), and advance their mind blade advancement whenever they advance their manifesting (consider same tier as Gifted Blade).  The similar optional rule for War Souls also applies.

See also 3.P Homebrew Magic Options.