With the U.S. Navy's New Orleans Data Center, we had a couple of ORACLE databases and more than one SQL Server database. We had a smattering of others, including perhaps one or two Sybase DBs. I don't recall any Informix or DB2 projects, but we were only the south-east regional data center. The Navy had at least three more regional data centers in San Diego, Norfolk, and Seattle. I understand there is a USMC (Navy-affiliated) center near Kansas City, but don't know much about it; it was under construction when I left. I know the Army and the Air Force have data centers as well, as does the Coast Guard. So I'm sure that everywhere you look you would find some oddball and some common DB systems.
These days, military folks most often go straight for web-activated DBs for which there are a gazillion web/DB tool sets, and Access doesn't do super-well on that front by itself. But Access is very good at providing in-house ODBC-based interfaces to a back-end database other than "native" Access format. At the same time, the web tools ALSO can work with that common non-Access back-end. Therefore, one of the most powerful in-house methods is the hybrid of Access front-end forms & reports but web-based outward-facing forms and reports as well, using a 3rd party database.
Now, 25+ years ago, there was a mainframe/super-mini product called SmartStar that was about as close to Access as you could get on machines that did mostly batch processing and not that much interactive stuff. It could only do character-cell graphics, forms, and reports - but it was very good at what it did. The problem, of course, is that time had passed by that technology but the Navy had economic reasons to stay with it LONG after it should have been discarded on the scrap heap. I retired about a year before the fourth hardware iteration of that system finally was shut down. By the time I had retired, all of the menu interfaces were web-enabled from ORACLE and ORACLE Tools. They were converting the remaining batch processes one by one, and my assistants could handle that system without my help. One year after I retired, they finished the job.
As far as small business products? With the Borland Paradox product now owned by Corel and with FoxPro having been bought out by Microsoft, there aren't THAT many small, general DB products. A LOT of vendors offer specialized pre-packaged systems. Take, for example, QuickBooks, which is a dedicated purpose DBM for a business with personnal, accounting, sales, and a couple of other components. But if you do a search on "small business database solutions" you see things that are MOSTLY based on SQL services plus whatever that vendor offers as a design package. I happen to think that Access still does the best job out-of-the-box as a small business solution. The ability of Access to work with other members of Office just strengthens its case.
The biggest negative factor in the mix is that the other Office components can be taught quickly. My wife used to teach Office components. Give her about two days and she would have you working with Word like a pro. Excel was another two-day situation. Outlook was one day to get started. PowerPoint was two days worth of classes and then done. But the problem with Access is that a week isn't enough to teach database design, and THERE is where things go south in a hurry. Oh, Access is pretty easy to use from the front-end mechanical viewpoint. BUT unlike some of the utilities, there are SERIOUS procedural consequences down the road if you have made bad design choices. The novice with Access can get something up and running quickly, true. But the more complex the problem, the worse it gets to develop.
Therefore, when you ask me whether there is another good product like Access - it's a diminutive comparison because there is NO product that will hold your hand and step you through the pitfalls of what you are about to build. Access just comes closer than some others, but it doesn't do that much better because of the nature of the problem to be solved.