The below recommendations are my personal favourites hand-picked for coaches, consultants and online service providers. All of them have been personally tested by myself and some of them I use myself for my own business.
Learnworlds is a robust Learning Management System that would be perfect for you if you have a B2B audience. The overall look and feel of it is more professional compared to other course hosting platforms.
New Zenler is an all-in-one platform (like Kajabi but at a quarter of the price) that combines funnels, emails and course hosting. It is currently an invites and offers a generous free plan. Sign up for free with my invitation link.
Thrivecart is a simple checkout solution that can be purchased with a one-time fee. It also has a simple landing page builder and course site builder and would be suitable for businesses who wants to validate an idea without spending much.
BLAB is my online booking system. While most people use calendly because it's free, I like to use BLAB as it offers additional features such as in-built landing page, multiple brand setup and the ability to accept payment.
If reviews and testimonials is important for your business, you need to check out Endorsal. They make collecting and displaying all reviews so easy with native integrations with Facebook & Google which means you can display all reviews on the same page.
Need an affordable, easy to use email service provider? Mailerlite is probably your answer. It is not as feature rich as their major competitors but is perfect if you're starting out and need a simple (and not overwhelming) email marketing solution.