I'm a Siemens PLC expert with 8+ years of experience, former Siemens employee.
Recently I developed a MES (manufacturing execution system) which would perfectly match your requirements. Please see a short description in my profile. It consists of two parts
1) .NET C# application which collects data from PLCs over Ethernet and stores to a MS SQL Express database
2) Web server which allow multiple users to monitor real time and archived production data.
The system was designed within 1 month entirely on free components - without OPC, WinCC, Archiver
With the Siemens PLCs the application can be redesigned to run on Linux.
Best regards,
Denis Poduzov