phpIPAM

phpIPAM is a free open source IP address management application, and it occupies the practical middle ground between managing addresses in a spreadsheet and buying an enterprise DDI platform.

That gap is real and widely occupied. A great many networks are documented in a shared spreadsheet that is perpetually out of date, because the alternative has historically been an expensive commercial product requiring its own project to deploy. A free tool covering the core function well is often the correct answer.

The functional set covers the essentials properly: VLAN management, VRF management, an IPv4 and IPv6 calculator, IP database search, email notifications and custom field support. IPv6 support matters more than it once did, and the calculator addresses the fact that IPv6 subnetting is genuinely hard to do reliably in one's head.

Custom fields are what let an installation match how a particular organisation actually thinks about its addresses, rather than forcing its records into someone else's schema. The project maintains changelogs, translations and current installation guides, including a complete walkthrough for deploying the latest stable version on Ubuntu Server with nginx. There is no licence cost.