Hi Alok,
It would be great if you can specify what are all the data you like to use in other software. Based upon the requirement you can choose it.
there are no.of ways to deal your requirement as I know few of them are below
1. Calling Std BAPIs/RFCs in your legacy software
2. Developing SAP RFC's for interaction for data
3. Web services
4. Generating Files either to application/presentation server
5. SAP ADBC connection (Using this you can write the data in other data base from ABAP coding)
Thanks
SaiKrishna