20 Web App Ideas by Type: Tools, Directories, Marketplaces and More

Twenty web app ideas grouped by type — calculators, directories, marketplaces, group tools and generators — with who uses each, who pays and the MVP to build.

Mythex Team · 2026-09-29 · 7 min read

The easiest way to find a web app idea that works is to start from the type of app, because each type has a known shape, a known way to attract users and a known way to make money. A calculator gets found in search and upsells saved results; a directory charges for listings; a marketplace takes a commission; a group tool charges the organiser. Below are twenty ideas grouped by type, each with who uses it, who pays and the smallest first version (MVP).

For personal projects to learn on, see side project ideas; for subscription tools for small businesses, see micro-SaaS ideas.

Web app types compared

Type	How people find it	How it usually earns	Hardest part
Calculator or tool	Search, sharing	Paid saving, exports, pro features	Standing out from free alternatives
Directory	Search, listings shared by owners	Featured or paid listings	Collecting good data at the start
Marketplace	Search, both sides' networks	Commission or listing fees	Getting buyers and sellers at the same time
Group tool	Invitations from the organiser	Organiser pays per event or per season	Each group is short-lived or seasonal
Generator	Search, sharing	Per batch, subscription	Output quality and design
Data explorer	Search, press, links	Sponsorship, pro access	Keeping data fresh

Pick the type that fits your skills and how you can reach users. If you already have an audience in a niche, a directory or marketplace can work; if you have none, a tool that search engines can send people to is often easier.

Calculators and single-purpose tools

1. Rental yield calculator for small landlords

For: People who own or are considering one or two rental properties.
Who pays and why: Landlords who want to save and compare properties, for a small subscription; the free calculator brings them in.
MVP: Inputs for price, rent, costs and financing, a clear results breakdown, and a saved-property list behind sign-in. Keep it an estimate tool, not financial advice.

2. Materials estimator for one trade

For: DIYers and small contractors — for example paint, tiles or decking.
Who pays and why: Contractors, for a branded quote from the estimate they can send to customers.
MVP: Room or area inputs, quantities with waste allowance, a shopping list, and a paid branded PDF quote.

3. Shipping cost comparison for small online sellers

For: People selling physical products from home.
Who pays and why: Sellers, for saved package presets and bulk comparisons; the single lookup is free.
MVP: Package size and weight, destination, a comparison of rates you have entered or can legitimately obtain, and saved presets. Check each carrier's terms before using their rates.

4. Event budget planner

For: People planning weddings, milestone parties or small conferences.
Who pays and why: The organiser, a one-time fee for the full planner; the basic budget is free.
MVP: Budget categories with estimates and actuals, payment due dates, and a shareable view for a partner or co-organiser.

Directories

5. Niche job board

For: Employers and job seekers in one field or region.
Who pays and why: Employers, per job posting, because a focused board reaches better-matched candidates.
MVP: Job listings with filters, a paid posting form, and an email alert for new jobs. How to build a job board covers the details.

6. Local specialist directory

For: People looking for a specific kind of provider — mobile vets, sign-language interpreters, accessible venues.
Who pays and why: Listed businesses, for featured placement and richer profiles.
MVP: Listings with location and filters, a claim-your-listing flow, and an enquiry form. See how to build a directory website.

7. Software directory for one industry

For: Businesses choosing tools in a specific sector, such as dental practices or event planners.
Who pays and why: Software vendors, for featured listings or lead forms — while keeping reviews and rankings honest.
MVP: Tool profiles with categories, side-by-side comparison, and a "suggest a tool" form.

8. Venue finder for one kind of event

For: Organisers of workshops, meetups or small offsites.
Who pays and why: Venues, for listings and enquiry leads.
MVP: Venues with capacity, facilities and photos, search by date and size, and an enquiry form that emails the venue.

Marketplaces

9. Equipment rental between businesses in one trade

For: Trades or studios with expensive equipment that sits idle — film gear, event furniture.
Who pays and why: A commission on each rental, paid by the renter or the owner.
MVP: Listings with availability, a booking request flow, owner approval, and payment through Stripe. How to build a rental marketplace covers the harder parts, including deposits and payouts.

10. Tutor matching for one subject

For: Parents or adult learners and tutors in one subject or exam.
Who pays and why: Tutors, through a listing fee or a commission on booked lessons.
MVP: Tutor profiles with subjects and rates, search, a contact or booking request, and reviews after lessons.

11. Used gear marketplace for one hobby

For: Enthusiasts buying and selling specialist equipment — climbing, cycling, music.
Who pays and why: Sellers, per listing or through a commission, because general marketplaces don't have the right filters.
MVP: Listings with hobby-specific attributes, search and filters, messaging, and seller ratings.

Group and organiser tools

12. Sports league manager

For: Organisers of amateur leagues.
Who pays and why: The organiser, per season, to replace spreadsheets and group chats.
MVP: Teams, fixtures, results, an automatic league table, and a public page for players.

13. Group trip planner

For: Friends or clubs planning a trip together.
Who pays and why: The organiser, a one-time fee per trip for extras like cost splitting and exports.
MVP: Itinerary, votes on options, a shared packing list and a cost tracker showing who owes whom.

14. RSVP and seating planner for events

For: Couples and event hosts.
Who pays and why: The host, one-time, because seating charts and dietary lists are stressful to manage by hand.
MVP: Guest list with RSVP link, meal choices, drag-and-drop tables, and a printable seating chart. How to build a wedding website is a good companion.

Generators

15. Certificate generator for course and event organisers

For: Trainers, schools and event organisers.
Who pays and why: The organiser, per batch or monthly, to avoid making certificates one by one.
MVP: Upload a list of names, pick a template, generate PDFs, and email or download them.

16. Invoice generator with saved clients

For: Freelancers who invoice a few times a month.
Who pays and why: The freelancer, for saved clients, branding and payment status; one-off invoices are free.
MVP: Invoice form, PDF download, saved clients and a paid/unpaid list. How to build an invoicing app goes further.

17. Digital signage for small venues

For: Cafes, gyms and reception areas with a spare screen.
Who pays and why: The venue, a small subscription, to show menus, schedules and notices without a USB stick.
MVP: Slides with text and images, a schedule for when each shows, and a full-screen URL to open on the screen's browser.

Data explorers and trackers

18. Public data explorer for one dataset

For: People who need a specific public dataset in a usable form — local planning applications, school inspection results, grant awards.
Who pays and why: Professionals who use it for work, for alerts and exports; sponsors may also pay.
MVP: Search and filters over the dataset, a page per record, and a paid alert when new records match. Check the dataset's licence first.

19. Price tracker for one product category

For: Shoppers in a category with frequent price changes.
Who pays and why: Retailers, through affiliate programmes where they exist and you meet their terms.
MVP: Product pages with price history, a price-drop alert, and clear disclosure of affiliate links. Respect each site's terms on collecting prices.

20. Changelog and status page host

For: Small software companies.
Who pays and why: The company, monthly, for a hosted page on their own domain.
MVP: Posts with categories, a subscribe-by-email option, and a status page with incident updates. See how to build a status page.

How to pick one

Choose a type that matches how you'll get users. Search-driven tools need SEO patience; marketplaces need a network on at least one side.
Narrow the niche. "A directory" is not an idea; "a directory of accessible wedding venues" is.
Name who pays before you build. Users and payers are often different — see how to make money from an app.
Build the one screen that delivers value and put it in front of ten real users.

Building a web app with Mythex

All twenty ideas are browser-based apps: forms, lists, a database, sometimes sign-in, file uploads or payments. On Mythex you describe the first version in chat, try it in a live preview, and publish it to a public URL. The app runs in the browser and adapts to phone screens; native App Store apps aren't available yet. A Postgres database is added when the app needs to store data, and payments, login and email are wired to your own providers. The templates and the docs' idea to live app walkthrough are good starting points.

Questions

What is a web app?

A web app is software that runs in a browser, so people use it by visiting a URL instead of installing it. Unlike a simple website, it usually lets users sign in, save data and do tasks, such as booking, calculating or collaborating.

Which type of web app is easiest to start with?

Single-purpose tools such as calculators and generators are usually the simplest: one screen, little or no stored data and no need for other users to join before it is useful. Marketplaces are the hardest because they need both buyers and sellers.

Can a web app work on phones?

Yes. A responsive web app adapts to phone screens and can be saved to the home screen as a progressive web app. It won't be in the App Store or Google Play unless you also build a native app.

How do web apps make money?

Common models are subscriptions, one-time purchases, per-listing or per-use fees, commissions on transactions, sponsorships and affiliate links. The right one depends on who gets the value and how often they come back.