Windows & IIS.
Database can be Oracle or SQL Server.

Thanks. What is the programming language used? (I know in Financials and HR, entire business logic is written in COBOL).

Which piece are you referring to? PSA/SA is not architected the same way as Lawson's other ERP products (it was acquired from another company--Account4). The base business logic is delivered as a compiled DLL on the web server. Additional business rules can be written in PSA's proprietary language, which is similar to Javascript. Integration with the Lawson ERP is done as database triggers.