on larger agriculture and industrial websites generally have the normal stuff. but if you get into the small mom and pop companies. they begin to offer a lot more variety.
look up attachments for "fork lifts" there be a lot of different attachments that have come about, due to many business needing a forklift to load/unload trucks. as a result you can find plows, buckets, different styles of forks, etc...
on the agricultural side, you can get into a lot of different style of forks and pushers. to deal with various animals, to dealing with different types of crops.
there is a couple companies that do sell 3pt hitch fork lift attachments.
and there are some FEL attachments for fork lifts that easily allow you to turn the forks upside down.
tele-handlers as someone already showed pictures of. you can find many attachments for them just like you can for a tractor and fork lifts, and skid steers.
most of the stuff i can remember over the years, ended up being google searches and clicking up on "images" to see what shows up.
i do remember a couple DIY builds, were they just pulled the FEL off, and stuck a fork lift to the front of the tractor. for better stability. err i take that back now that i think about it. one of the builds they reversed the seat / stearing wheel and drove it backwards. the front pivot point = to much action left to right and possible tip over.