Awk is a POSIX-standard command line tool and programming language for processing DSV data. If you use Linux, macOS or a BSD, you almost certainly have it installed. See below for Windows.
If you already know how to program, the nawk man page is a great way to learn Awk quickly. What you learn from it will apply to other implementations on different platforms. Read it first if you feel overwhelmed by the sheer size of the GNU Awk manual.
A Python library with a CLI. Convert between a number of file formats for tabular data: CSV, XLS, XLSX, ODS, and others. Query the data (via SQLite). Combine tables. Generate schemas.
Use header row for column names. Custom input and output encoding. Custom input field separator. Custom output field separator. Custom output formatting. CSV JOINs. Python module. Excel and JSON to CSV. CSV to JSON. SQL queries for CSV.
Use header row for column names. Column name aliases. Can skip lines until a regexp matches. Custom input field separator (string literal, per-file). Keep SQLite file. Show generated SQL. Table JOINs.
Use header rows for column names. Custom field separator (regexp). Custom record separator (string literal). Lines as columns. Skip a given number of lines and the beginning and at the end. Merge selected columns into one. HTML, CSV, SQL, and Tcl output.
Create and manipulate JSON with a DSL inspired by Rust, C and JavaScript. Similar to jq. Supports JSON, YAML and TOML as well as binary formats like Apache Avro and MessagePack.
Set and remove properties in INI files. Retrieve properties as shell script commands to set the corresponding variables. Outputs updated INI data or changes files in place.
Set and remove properties in INI files. Retrieve properties as a list of batch file set commands to set the corresponding variables. Changes files in place.
Query and modify a number of file formats. Not all of the formats are equally well supported by Augeas and for some only a limited subset of all valid files can be parsed.
Query and modify configuration files. Shares Augeas' limitations when it comes to application-specific configuration files (it uses the same lenses), but has better support for generic formats such as JSON and INI.
Firebird is a FOSS database that can be used from a single file, like SQLite. "isql is a program that allows the user to issue arbitrary SQL commands".