A double-entry bookkeeping computer language that lets you define financial transaction records in a text file, read them in memory, generate a variety of reports from them, and provides a web interface. In theory, if it can read a text file, it can manipulate your accounting "database." More of a standard or file format than an application because you can do it all in a text editor if you really want.
The reference implementation is written in Python and seems to have a webapp.
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