This is a very general question. Call it a thought bubble.
I have a client who has a very old legacy system (Tetra CS/3 running on Unix) with lots of modifications unique to their business. They need to update at some stage but will have a huge problem re-engineering all of the changes. For this reason package software may not suit and we are considering rewriting the entire system using a combination of SQL Server and run-time Access databases in a type of client/server relationship. The basic accounting functions are not that complicated, which is why I feel confident about re-writing the applications. I know I can use SQL Server Express to create a small configuration with just a few users and then migrate to full SQL if it works or use a cloud-based database. Ultimately, they'll want to have about 20-30 users with half of those being active at any one time.
The question is whether or not it is feasible to use a run-time MS Access database to provide this type of solution for each user. Virtually none of them will require massive amounts of data transfer; they mainly just do order entry and processing, receipts, payments, etc. I've seen a company run it's entire data processing needs on a series of Access databases before, so I can see it can be done, although I suspect that standard Access does not provide the sort of robust data integrity necessary, hence the SQL server.