I am in no way affiliated with this product. Yesterday I was thinking about exactly this problem. I'm a solo freelancer in the data space, so my projects always include a mix of technical and managerial/ general project management problems. I normally do a single "assessment" day with a client to check the status quo of things. Having the structure of a template I can easily run down immensely helps to reduce cognitive load to be structured and in effect helps me to render a more professional service.

The app is minimal in it's layout and very clearly structured. You can create templates, either with single tasks or section lists and create a checklist from a given template. While not relevant to me, there is also a team functionality.

Classic case of do one thing and do it well.