They all use variations of DPoS. EOS is a generic implementation of Steem. It can be used to take care of logistics for hospitals, manufacturing of all types, and ultimately I believe that some later implementation of EOS can replace the Congress and US Senate. The office of president is already obsolete and really at this point, government runs mostly without the need for a president. The presidency is becoming similarly obsolete to what the Queen of England is. Dan Larimer is creating a new system of governance similar to what Ben Franklin did over 200 years ago. The new "founding witnesses" will be like the old founding fathers of a new republic.
Both Steem and Bitshares will be able to interact with EOS in performing atomic swaps, but you should know that Steem and Bitshares are special use cases with hard coded conventions. EOS refactors many routines to accept a generic version of implementation. It is an OS similar to DOS for Windows or UNIX for MacOS and Linux.