Hi,
I have over 11 years of industry experience in ASP.net, C#, VB.net, SQL Server, MS-Access, MySQL and Oracle.
I would like to suggest you to go for a web solution. The web application can be used on any operating system like Windows or Mac. Also it is very easy to maintain since you need to install the program on every computer.
I can develop an web application for you in ASP.net using MVC. Where I'll convert all your existing data in SQL Server database. The existing data can be convert into SQL Server database by writing ETL routines.
If you want we can discuss this detail.
I look forward to hearing from you.
Regards,
Farooq