MicroRIM's R:Base had modest success, pre client/server. It was always a true RDBMS. I had used R:Base for "real work" and dBase (and kin) for flatfile type stuff.
I've always wondered how Oracle swept the industry, and R:Base did not. Probably multiple factors.
Like Oracle's initial customers had big iron and those enterprise contracts are big money. Whereas R:Base was part of the personal computer revolution and so probably wasn't even considered.
In my mind, MS Access was the market fit successor. IIRC, Access was the first "workgroup" (network file sharing vs true client/server) RDBMS to make the jump to GUI. A bit like Excel displaced Lotus 1-2-3.
Too bad. Much as I came to love Access, I also loved R:Base.
IBM IMS goes back to 1968 (originally developed for NASA). Cincom's TOTAL was sometime around the early 1970s. I'm sure there were databases on DEC's PDP systems. And so forth. dBase II was an important early database product for CP/M and then DOS systems but there were many earlier databases on mainframes and minicomputers.
> there were many earlier databases on mainframes and minicomputers
We were talking about commercially successful DBMS. From the Wikipedia-page it is still not clear to me when IMS became a DBMS for example. Wikipedia lists TOTAL as released in 1982.
IMS was always a database. But it was hierarchical rather than relational. I was thinking TOTAL was earlier than it was though given the company had been in business for quite a while.
What is true is that pretty much all the earlier database products were tied to specific system hardware. In fact, Cincom (which developed TOTAL over time) was arguably the first independent software vendor. So there were lots of databases being put out by successful computer companies (indeed most of them). They just weren't products you would buy or use unless you were also using a particular manufacturer's hardware.
TOTAL was around and already considered old-fashioned (because it was hierarchical rather than relational) in early 1981, when I persuaded my boss not to use it.
In computing history claims like "first" and "commercial success" need to be qualified and defined, and therein things become difficult since timing and thresholds matter to meet a generally acceptable standard of either claim.
In the 1960s, several companies were selling commercial database management systems (as a distinct product), for example: IBM IMS, Univac DMS and General Electric IDS. These ideas were established to a level that there was a database standard committee known as CODASYL active from 1959 onward.
For me, only Oracle comes to mind.