Ask HN: What are MS Access's biggest competitors?

I'd say it's mainly SQLite by itself over Libre/Open Office or Kexi or Glom because the others don't have viewers and SQLite is bundled with mobile devices and operating systems.

Of course, the comparison may seem odd given that Access has a GUI and SQLite is just the database engine but some consideration should be given to the fact that people who operate databases often know how to use SQL commands and won't have any problem learning scripting languages to build applications to ease data entry. Software like GAMBAS makes that easy on Linux. Access users should have no trouble converting to GAMBAS at all.

But for casual use outside of custom applications design Libre/Open Office are the biggest threat to Access.

MS Excel

In practice I've seen Excel by far as its main competition followed by FileMaker Pro, but the latter not nearly as much as people simply using the spreadsheet.

There is at least one YC W13 company that is working on removing the Big Ol' Excel sheet of company passwords, in case you were asking with respect to startup business ideas.

FileMaker Pro, but it's expensive.

Filemaker