Ask HN: What are some cool self-hosted tools like Sendy?

Amid the ever-growing number of subscription SaaS companies, I love that there are still awesome self-hosted tools like Sendy (bulk emails using AWS SES for delivery) out there. What are some other one-time-fee self-hosted products that rock?

I'm not affiliated with Sendy, I'm just using it as an example of a tool that is still actively developed and that has resisted the temptation to switch to a subscription model.