Alibaba provides an online platform for buyers and sellers, or rather multiple platforms, depending on the seller. It offers free seller posting to attract small sellers, provides subscription and commission based listing service for brands and niche markets, and it provides a connection between buyers and sellers, offering them commission-based trading.
The free-post based service is targeted at small sellers and has attracted millions of such sellers. While there is no fee for product listing, sellers must pay for their advertisements to make their product listings more attractive. Millions of sellers have so far listed a few hundred offerings on the site, Taobao.
Tmall is targeted at niche markets where consumers buy branded products. Here the top global brands like Apple and Nike pay for listing (through annual subscriptions and deposit fees) and pay for trades. Here the rapidly rising middle-class and upper-class shop.
Alibaba itself connects mainly exporters and importers for listing and charges them for trades, thereby connecting Chinese exporters to the other companies of the world.
Thus domain-specific services are provided by Alibaba.