What are the different ways available to get access to the data from the Progress procedures in the form of JSON? Other than creating PASOE instances, ODBC or JDBC? If I want to build an API that can communicate with Progress 4GL DB, what are the options available other than what I have mentioned above? Just to give an example I have a front end application which is build on JavaScript/Angular/ASP.NET CORE and if I want to make calls to Progress DB, how do I achieve it? It would be helpful if I can know any latest technologies that can be integrated to communicate with Progress 4GL DB.
If you run old-school appserver or webspeed you can set up a webservice that way.
For .Net (or Java) you can check the Open Client: https://docs.progress.com/bundle/openedge-open-clients/page/Introduction-to-Open-Clients.html
You could also develop some kind of server operating on a socket but I think sticking to tested techniques such as those you mention NOT wanting to use is the winning bet. Whatever you save in money not licensing PAS (if money is the issue) will be losts in time developing that server.