Lots of things! But here are some general examples:
A directory-type app, e.g. one where founders in an accelerator can curate their own profile, see the other founders, and find out what products they’re using in their company
A jobs-on-demand app, e.g. one where workers are assigned research tasks with a short brief and a due date
A catalogue of stuff, e.g. a list of spaces that someone might want to rent for a conference, and the ability to favourite, write notes, and enquire
A project tracking app, e.g. where SEO specialists can see the status of the clients they have, any tasks required for each client, and what’s assigned to them
An informational portal, e.g. where a wine collector can see the info about bottles being held for them, their estimated value etc.
A requests portal, e.g. where farmers can request for a drone company to take aerial photos of their fields, and see the results
A CRM-type portal, e.g. where a VC can see the companies who are applying to them, view the company info/pitch deck and see a history of any meetings they had with them.
An application form portal, e.g. where someone applying for government funding can sign up, fill our their application, and then see whether it had been accepted
A resource center portal, e.g. where a new student at a university can see all the local restaurants that give discounts, read helpful articles about campus, and see FAQ