12 Useful Ways to Reuse an Old Router

1. Wireless repeater
2. Guest Wi-Fi connection
3. Cheap internet radio
4. Use the old router as a network switch
5. Adapt it as a wireless bridge
6. Convert your router into a NAS
7. Use an old router as a web server
8. A DIY VPN router
9. Sell the router on eBay
10. Set up a separate network for IoT devices
11. Learn more about home network
12. Donate it to a church or school

Source: https://www.makeuseof.com/tag/ways-reuse-old-router/