I'm looking for a library or method to generate addresses for as many of the most popular currencies/altcoins as possible. Is there a known library that supports this? Or do I need to use a specific client for each coin?
It doesn't generate wallet addresses by coinname, but instead by the leading character within the wallet address. I get these from the block explorer for the coin, looking at top address.
http://www.universalwalletgenerator.net/ lets you do it by coin name.
You should find libbitcoin's bx command line interface to be quite useful. The code line references BIP44 Altcoin Version Mapping Table might be a bit stale, but the content of this table has strong trace-ability. Example 7 through Example 11 should get things going quickly. These examples merely extend the initial work documented by Andreas M. Antonopoulos in Chapter 4.