A modern way is to create a
REST API, you could use ASP.NET Core for this.
See:
best-web-frameworks-to-create-a-web-rest-api~asp-net-core[
^]
ASP.NET Core has a bit of a learning curve though, if your needs are simple using a database and network is fine.
You might also be interested in
NSwag[
^]
If you have a PostgreSQL database creating a REST API is very easy with
PostgREST[
^]
Another option is using
WCF (Windows Communication Foundation), if your applications don't need internet you can use self-hosting, see:
Self Hosting in WCF[
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It is not safe to expose a self-hosted application to the internet, in this case you need IIS and things will get more complicated.