Sometimes I am dealing with prospective customers that have never heard of FileMaker and that raises questions as to FileMaker's legitimacy. Not that these customers would recognize a real database engine name, but they recognize the big software company names such as Oracle, Microsoft and IBM. Of course we can always throw around that FileMaker is an Apple subsidiary and everyone has heard of it.
There is an Austrian company called "DB-Engines" that does a monthly ranking of databases. They are probably not unbiased in that they are a commercial database company and not a non-profit or educational institution. But that have a formula they have developed to search the internet to compare the relative popularity of different databases. This is more a measure of the social network relevancy of different database software names than say number of users or storage amounts or other measures you might use. But they run the report each month and it is an interesting thing to compare.
For September 2014, they found 223 database engines and of them, FileMaker ranked 14th. Clearly FileMaker is not at the top of the heap, but 14 is fairly respectable in my opinion. The ones ahead of it were Oracle, MySQL, MS SQL Server, PostgreSQL, MongoDB, DB2, Access, SQLite, Cassandra, Sybase ASE, Solr, Redis and Teradata. A few of those are not traditional relational database that would compete with FIleMaker. Some are Document stores or search engines, etc.
Feel free to read up on the ranking and method of ranking at: http://db-engines.com/en/ranking