Wallet (CLI-only): https://github.com/steemit/steem

The web wallet/site/app that runs on steemit.com is also there now (was released a bit later)

I guess because I figure they premined a whole bunch of tokens for free whereas the rest of us have to buy them. But maybe I'm even wrong about that. How was the initial distribution done?

I still don't quite follow the logic on why that makes the inflationary STEEM token itself good for them, when everyone else can avoid the inflation by using SP too. If anything, given their large SP holdings, the restrictions on liquidity of SP hurts them as much or more than anyone else, but in any case, here's some info about the launch.

It was effectively (but not literally) an 80% premine (though not quite free; they had to compete with a few other miners and did apparently spend money to do this). They launched with a public bitcointalk thread (still there) but there were no instructions or other information so only those able to figure it out from the code were able to mine it. It was openly stated at this time why the developers were doing this.

The plan (then and now) for the 80% is to give away 40% (every new account needs coins and receives a minimum balance–currently 3 SP–for free), keep 20%, and sell 20% to pay for development. This process is reasonably transparent and can be tracked by watching the 'steemit' account and the ones fed from there ('steem' creates the new accounts for example).