https://plaintextaccounting.org/
Especially because there is a wide range of apps, ranging from CLI to web and even mobile, which can be used for PTA and due to the fact that they acknowledge the same standard are interoperable:
https://plaintextaccounting.org/#software
The most well known ones being
- hledger (https://hledger.org/),
- beancount (https://beancount.github.io/),
and
- ledger (https://ledger-cli.org/)
Important note: All free and open source