Surprised you didn't include Zoho Creator
Great list, and there were two I didn't know about, so thanks for the diligence. I'm surprised that you missed Zoho Creator, though. Zoho has a pile of tools for SaaS-type leanings, including CRM and so on, but one that seems to be under appreciated is Zoho Creator. It's very similar to Quickbase, in that you can quickly build data-centric apps around a simple form, and then customize and enhance as you need. I built a database system for a non-profit (via Taproot assignment) using Zoho, and then when it quickly gained steam, was pleasantly surprised at how powerful and feature-rich Creator turned out. I was able to build a rich application with many different views, reports and forms, tracking multiple parts of their business, and even include workflow capabilities, email notification and web forms. Zoho Creator was far more powerful than I originally thought, and since then I've now created dozens of applications solely within their toolchain. Best of all, they offer a free tier (up to 3 apps) that works perfectly for small businesses. This one should definitely be on your list for the next time...
Second, I would put a plug out for the Oracle Application Express (Apex). It's a RAD environment that is focused on building great Oracle-based applications. It's also free for up to 5GB (or 50GB? can't remember!) databases, using Oracle XE. Apex is the development tool, and is totally free. Anyhow, if you have on-prem needs and want a solid database, then Apex is an excellent option. You can keep it very simple, or go very deep, depending on your needs on both the UI and backend side. They have a very active support community as well, and ODTUG also sponsors an active training and forum-based community for Apex. It's a bit different from the other offerings in your list because it's more like Filemaker (from the perspective of on-prem hosting and app dev), but still something that many small businesses may find to be a perfect fit.
Thanks folks! -Bruce