'All-in-one' gets used loosely in software marketing, so it's worth being precise about what it actually means here: one login, one bill, and your customer, invoice and project data living in the same place instead of being copied between separate tools by hand.
When one tool genuinely makes sense
Not every business benefits from consolidating. If you've got a specialist tool that your team loves and is genuinely excellent at one job, replacing it with a more generic all-in-one feature can be a downgrade. The case for switching is strongest when you're stitching together three, four or five separate subscriptions and spending real time keeping them roughly in sync.
The tell-tale sign is re-entering the same information more than once, a customer's details in your CRM, then again in your invoicing tool, then again in whatever you use for projects. That duplication is exactly what an integrated platform is meant to remove.
Zoho One
Zoho One bundles most of Zoho's individual products, CRM, invoicing, projects, and a fair amount more, into a single subscription. If you're willing to live inside the Zoho ecosystem, it's genuinely comprehensive and reasonably priced for what you get.
The scale is also the challenge. There are dozens of apps in the bundle, and most small businesses only ever touch a handful of them. Expect a longer setup than a purpose-built small business tool, simply because there's more there to configure.
Odoo
Odoo is open-source at its core, with modules covering CRM, invoicing, inventory, projects and manufacturing, among a lot else. Because it's modular, you can start with just what you need and add more later, and there's a genuinely free tier for a single app.
The flexibility is also the cost. Odoo tends to need more setup work than the other tools here, and businesses without any technical help on hand sometimes find themselves paying a partner to implement it properly.
Bitrix24
Bitrix24 bundles CRM, project management, a basic helpdesk and internal collaboration tools, with a genuinely generous free tier for smaller teams. For businesses wanting breadth without much upfront cost, it's one of the stronger options.
As with the free CRM plan, the interface can feel busy, and it takes a bit of patience to find your way to the features you actually use day to day among everything else that's bundled in.
Before switching to any all-in-one platform, list out exactly which tools you're currently paying for and which features from each one you actually use. It's a quick way to see whether you need breadth or just need three specific things done well.
WeekOne
WeekOne takes a narrower, more deliberate approach than Zoho One or Odoo: rather than bundling dozens of apps, it covers the specific set most small UK businesses actually need, CRM, quotations, invoicing, projects and support, and keeps that set tightly connected.
The trade-off is scope. If you need inventory management across multiple warehouses or manufacturing workflows, that's not what this is built for. For a service-based small business running leads through to invoiced work, it covers the whole journey without the setup overhead of a bigger, more general platform.
Picking between them
If you want maximum breadth and don't mind a longer setup, Zoho One or Odoo will get you further, eventually. If you want something running properly within a day or two that covers the core of running a small service business, that's the gap smaller, more focused platforms like WeekOne and Bitrix24 are built to fill.