SuiteCRM

SuiteCRM is what happens when a commercial CRM is forked and then maintained in the open for more than a decade. It is a full business system rather than a light one — accounts, opportunities, quotes, campaigns, workflow and reporting are all present — and the whole thing is available under an open-source licence at no cost per seat.

That combination is why it scores where it does on value. Nothing about your customer records has to leave hardware you own, the source is there to read, and the ceiling on users is whatever your server can carry rather than whatever a price list says. The 8.x line is still shipping point releases, so this is a maintained project rather than an archived one.

The cost is the first day. Setup is a server installation with a database behind it, not a signup form, and the interface carries the accumulated design decisions of a product that started in the 2000s. A small team without anyone comfortable administering a server will find the free licence is the cheap part, and the newer open-source projects in this field are considerably easier to stand up.