F-Droid repos generally maintain support for old F-Droid releases for a long time. That means that old F-Droid releases will continue to work for years. That provides a path to run F-Droid on very old Android releases. Here are the download links for installing the newest release that runs on a given Android release:

• Android 6.0 (API 23) and up: F-Droid (latest stable)
• Android 5.1 (API 22): F-Droid 1.15.6
• Android 4.0 (API 14) to Android 5.0 (API 21): F-Droid 1.12.1
• Android 2.3.3 (API 10) to Android 3.2 (API 13): F-Droid 1.2.2
• Android 2.2 (API 8) to Android 2.3.2 (API 9): F-Droid 0.100.1
• Android 2.1 (API 7): F-Droid 0.91
• Android 2.0 (API 5) to Android 2.0.1 (API 6): F-Droid 0.69
• Android 1.6 (API 4): F-Droid 0.56
• Android 1.5 (API 3): F-Droid 0.45

Please note that many apps on F-Droid may no longer support such old Android versions. It is recommended to enable the “F-Droid Archive” repository in the F-Droid app. Enabling the archive lets F-Droid show you older versions of apps, which may include versions that still work on your device.