IBM has relaxed the memory restrictions on the free version of their flagship database. Version 10.5 of DB2 Express-C can now use up to 16 GB of RAM. The product already allowed for unlimited database sizes on disc but is limited to a single socket (2 cores).
By contrast, SQL Server Express is limited to 1 socket (4 cores), 1 GB of RAM, and 10 GB of storage. Oracle 11g Express is likewise restrictive with 1 CPU, 1 GB RAM, and 11 GB of storage.
DB2 is available for Windows (x86/x64), Linux (x86, x64, Power Systems), Solaris, and OS X. DB2 can be managed from the command line or with the free tool, IBM Data Studio.
For DB2 training IBM is promoting the site Big Data University. In addition to DB2, there are courses for Hadoop in English, Portuguese, Spanish, and Russian. Most of the courses are free and some come with extra benefits like gift cards for Amazon Web Services.