Semicolons are the most common alternative to commas because they sidestep the European Excel locale problem. In German, French, Spanish, Italian, Dutch, and most other continental European locales, the comma is the decimal separator and conflicts with comma-delimited CSVs. A semicolon-delimited file opens cleanly into columns on those installs without invoking the Text Import Wizard. If you are sending data to recipients in continental Europe, semicolons are almost always the right default.
Tabs are common in scientific computing and Unix pipelines. The TSV (tab-separated values) format is essentially CSV with tabs, and tools like cut and awk handle tab-delimited files natively. Tabs also reduce the need for quoting because data values rarely contain literal tab characters, which makes TSV output cleaner and easier to read in a terminal than quoted CSV.
Pipes are common in log-style data and in some database export formats. The pipe character is unlikely to appear in data values, which again reduces quoting noise. Pipe-delimited files are easy to grep, easy to cut, and easy to scan visually. If your downstream tooling is a Unix pipeline, pipes are often a better choice than commas.
Custom characters serve niche use cases where the data contains all common delimiters. A file containing free text with commas, tabs, and pipes might use a rare character like the ASCII Unit Separator (US, decimal 31) as the delimiter to guarantee no collisions. FixTools accepts any single character as the delimiter, so even unusual choices are easy to configure.