Unsworn shaman. Possibly the best out of the shaman archetypes imo. That along with the lore spirit and the hex in it, arcnane enlightenment.
Paragon surge is a spell that gives you 1 bonus feat when cast, but subsequent castings untill you rest is the same feat. Ive seen some mileage come from this.
Oracle's spirit guide archetype gets floating things galore
* Sorry I didnt mention a the names I forgot some of them, but they shouldn't be to hard to find.
There is a feat that let's you get Weapon Focus with weapons that fall under weapon familiarity after 10 min. So an elf can have Weapon Focus (Branch Spear) then 10 min later have it be Weapon Focus (Curved blade).
Illusion spells, more specifically Shadow X spells, let you cast a version of any spell the fits the pre-reqs (and its chosen at cast time not at prep time).
There are also a number of archetypes that let you cast spells from other lists. Some of the archetypes even have the spell be free floating until cast for the day. Archetypes: Spell Sage Wizard, Mangambryan Arcanist, and there may be others.
Vigilantes have a Talent that is similar to Martial Flexibility, but it only works got Racial feats.
There is a spirit feat that let's you change the bonus it gives every day.
And things that deal with Harrow decks like the Tarrot Student Arcanist gives random bonus when used.
I believe Story Summoner might get an eidolon that can change its base shape and evo points.
Side note on Martial Flexibility - beyond the brawler and eldritch scrapper these archtypes offer the feature: Fighter Martial Master, Fighter Varisian Free-Style Fighter, Oracle Warsighted - and Belt of Superior Maneuvers is pretty cheap for an extra use.
Spells: Mnemonic Siphon, Plundered Power, Spellsteal
The Bloodrager- Prowler at World's End - gets to choose from different spirits that grant different powers
Sandman Bard can steal spells
There are a number of Spell Storing item (e.g Ring of SS) that others can store a spell in and you can later cast.
A Crossblooded Sorcerer can slip a Robe of Arcane Heritage on and off to good effect.
a skald get spell kenning which allow him to cast any cleric\wizard\bard spell of a level he can cast 1/day at level 5 more as he levels.
he also can get and give rage powers to allies
-my go to is summon a lot of creatures and give them stuff that ether work once per rage or work when they die (like the 'Linnorm Death Curse, Tor' rage ability +1 fire damage to their attacks and anyone who kill them must save or get fire vulnerability and be permanent staggered)
a ninja with the Forgotten Trick can gain other ninja tricks that it doesn't know.
btw about brawlers or people taking 'bar-room brawler' feat. i use it to pick up the dedicated adversary feat for a +2 fev enemy bonus against said race, i much prefer taking that feat in such way then taking it normally as a permanent feat(this way you are not stuck with a useless feat when other kind of enemies show up).
A note about shamans with arcane enlightenment. While it seems against the spirit of the limitations in that hex, there's nothing RAW (that I know of) which stops a non-lore shaman with wandering hex switching the spells the hex grants daily.
Masked performer bards get a weak form of martial flexibility.
Shadow mystery oracles can get a revelation to learn some shadow sorc/wiz spells, and can change the spells so gained each oracle level.
Wishes, including limited wishes, can substitute for other spells. Including ones you wouldn't otherwise be able to cast.
The evolution surge line of spells can change an eidolon temporarily, and there's a spell named transmogrify eidolon or something like that to change an eidolon permanently.
Mediums get to change their character daily.
The terrakineticist archetype gives kineticists different powers depending on the terrain they're in. OK, it's fixed for the character, but it'd look like a different character if it jumped off a dock into the sea or something like that.