I don't know of any existing ones offhand, although there are some. Surprisingly, the hardest part of making an RPG engine is multithreaded speach (lots of possible replies which change the whole outcome of the game).
what part of the 'RPG engine' are you talking about?
"Say you're hanging from a huge cliff at the top of mt. everest and a guy comes along and says he'll save you, and proceeds to throw religious pamphlets at you while simultaniously giving a sermon." - Dustin G
If I had the time, I'd make one. I tried making a zelda-style one, but lost interest. The original idea was for it to be entirely moddable (EVERYTHING, including the events and structure for the levels, were stored in external files, as were the tilesets, character sets, sounds, music, even screen layouts).
I got an RPG engine, well, half an RPG engine that you could use, if its the fighting you want. the graphics are what i would refer to as "poo" but you can change em. you can down load from...
"http://www.geocities.com/kyecansdale85/Tr.html"
The fighting style is a very basic on, completely automatic, some of the enemy HP is deducted every few seconds the amount depending on your strength, and you hit depending on your accuracy level, so for example if your accuracy was 50 and your strength 3 then every 2 seconds, a counter will be set randomly between 0-100, if its lower than your accuracy, you hit, if its higher you miss.
I also got a leveling up formula, thats pretty self explanitary though. hope it helps.
If you've been paying attention to the boards, I'm making a battle engine. It not finished yet due to computer lockout. but you can attack now. I'll let you know when its finished.
All platforming problems can be mostly solved here: