Jira alternative
Fuck you, Atlassian. People need a better UX for such apps as well as a stable functionality.

Images recognition as a service
In this case, as paid API.

Automating directory
A place where gathered tools that help people automate different things such as creating website, connecting it to Google Analytics, paying for the domain/hosting.

Job board for school students

Challenges social network
The platform that allows it’s users to create challenges, share these challenges with others and accept a challenge.
You can challenge your friends to pour a bucket of iced water over their heads to create awareness for an illness or you can challenge them to put on crazy Halloween makeup and reward the best with a free tickets to a horror movie.

Curated list of blogs
It's hard to find good blogs to read on a daily basis. The website can contain such categories as software engineering, business, health, etc.
Monetization: ads or paid weekly newsletter.

Advanced keyword planner
Helps you to choose popular keywords that in use by not so many competitors; proposes alternative keywords; shows who those people (age, gender, preferences) who search the keywords.

How much money would you spend for the solution (monthly)?

What do you think about new post format where you can choose how much money would you spend on an idea's solution? This can tell us how many people interested in it.

Reddit newsletter
The tool sends your choosen subreddit posts (all/top) every day/week by email.

EDIT: it's more convenient to not make a paid subscription, but to add ads/sponsor links to emails.

How much money would you pay for this?

Smart music player
The small device attached to a head listening human's brain waves to understand what music he/she likes. Can be connected to a phone via Bluetooth/WiFi.

How much money would you spend on the device?

Logo generator
The service will provide you a logo you choose among generated ones if you watch ads.
Monetization: ads, subscription (disable ads), one-time payments.

Prices tracking
The tool allows you to track prices on many sites provide house/cars rent, avia tickets, etc. The main difference from similar services is you can set up what notifications to receive on prices change: sms/phone/messenger/email, the interval to monitor, what sites to track and so on.

House manager
The system of sensors, mechanisms you can set up on house/flat, like a smart house, but it is a platform where you can download and install necessary software for the house's system (security algorithms, etc.). There are a community, free/paid software.

How much would you pay for this?

Kickstarter for cinema
Allows people to vote for movies/cartoons plots, ideas, sketches and donate for it, therefore other people or author can produce a movie. Also, people can subscribe to your movie's page, create logos, trailers, prototypes of characters.
So, you can create a page with your movie's idea, write a plot and wait for other people' feedback. Maybe, you will receive some money or there are will be people who are interested in a idea and going to sponsor/produce a full film.
Monetization: ads, donate fee.

How much would you donate for your own (or other person's) movie idea if you like it?

Fitness challenges
Compete with friends and other users in fitness training, track your/others progress, train together by scheduling and locating your next workout.
Monetization: subscription to premium features, gyms sponsorship (you can create ads for them as well).

How much would you pay for subscription?

Personal finance applications adapted for couples
Most personal finance apps operate on single-player mode but the reality is that many people share their financial lives with their significant others. What apps out there make it easier to share/split expenses, bills, savings, contributions, joint tax filing, etc.?

How much would you pay for it?

Instagram image quote generator
Allows you to upload image(s), the app scans them and generates matching quotes, based on what it saw on image(s).
Aimed for people who are busy by scheduling/creating many posts per time.
Monetization: one-time payments, subscription.

How much would you pay for it?

Restaurant cashier's automation
Self-serving kiosks for some reason are still not a thing. People are afraid of automation but to be honest there needs to be some automation. Hopefully, some of those savings can be passed on to consumers!

Multi-language Grammarly
"I really wish Grammarly was available in languages other than English. I used to be fluent in French but now I don't feel very confident when I am writing formal emails or other documents. I can't imagine I am the only one that goes through this."

Smart TV movies app
The app provides free movies/series, ability to download torrents. Can be ads, but in terms of 1 ad video per movie (or 2-3 ads if it's a high quality movie, like 4k).
The problem is current apps have inconvenient design, bad functionality, a lot of ads and paid subscription.