Is there any open-source project or 3rd party with reasonable fees that would allow deposits to my centralized exchange? Best with support for a wide variety of altcoins.
Your question needs more clarification. Are you looking for a bitcoin payment processor where you manage an online website, store or service, where users make altcoin or bitcoin deposits and you want it to appear as deposits to your centralized exchange?
If that's what you're looking for, this is a good list
https://bitcointalk.org/index.php?topic=5444578.0I prefer
https://coingate.com/ They have better solutions except they require you to verify your identity.
If this is not what you are looking for, should you ask about a cryptocurrency wallet? Or what specifically?