I recently came across an AES encrypted string and I was wondering if there was any program that can help me crack it.

If not, why? And wouldn't it be optional for the hashcat devs to code a program for cracking symmetric encryption algorithms like hashcat does with Hash functions?

My particular encrypted string uses base64 encoding
Well first of all hashcat is open source so, you could be the dev that codes an AES modul for hashcat.
Second point is, its probably not called HASHcat so it can crack non-hash encryption.
Last point, coding a simple program with Python, or what ever, that decrypts AES shouldnt be that difficult.
It won't be super efficient but it will do his job, or just google it. I'm pretty confident that you will find something.
You can't crack an AES key with naive brute force, period.

Even the shortest type keys have a keyspace so vast that it would take billions of years despite using all GPUs on the planet. And there are no shortcuts: Never any "easy" passwords that you can guess, like IloveSarah2015.

Also, a "key cracker" would have no way to know when it found the correct key unless you know a good part of the plaintext.
Only under certain circumstances (e.g. known plaintext attack) it is possible to crack the AES key. For WPA2 there is such an attack using ARP packages. You can find more on this topic in this paper
Wouldn't it be possible if you knew the entire output was ascii for example?
Then it could show you the ascii results?
It's still impossible to brute force 2^128, let alone 2^256.
Oh, I assumed you know the key, my bad. If you dont, ignore the last point of my previous post.