Here is the full list of all 36 FINAL FANTASY VII achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Reach level 99 with any character
Complete the second part of the game
Defeat the Diamond Weapon
Reach the maximum level of any Materia
Use Cid's 1st limit
Use Yuffie’s 1st limit
Complete the first part of the game
Use Vincent's 1st limit
Get Vincent on your team
Get Yuffie on your team
Use Red XIII's 1st limit
Use Aeris's 1st limit
Use Tifa's 1st limit
Use Barret's 1st limit
Use Cloud's 1st limit
Win your first battle
Complete FINAL FANTASY VII
99,999,999 Gil
Get Cloud's last Limit Break
Get Barret's last Limit Break
Get Tifa's last Limit Break
Get Aeris's last Limit Break
Get Red XIII's last Limit Break
Get Yuffie's last Limit Break
Get Cait Sith's last Limit Break
Get Vincent's last Limit Break
Get Cid's last Limit Break
Get materia Knights of the Round
Get materia Bahamut Zero
Defeat the Ultimate Weapon
Defeat the Ruby Weapon
Defeat the Emerald Weapon
Master all Materias
Get a Gold Chocobo
Use Cait Sith's 1st limit
Start a battle in the Battle Square