Yep, happened since yesterday for me.

This was first used in an iMac product page in 2014.

You can either do the above pricing, or if your premium feature is large enough. Price it like an add-on.

$X/user past 5.

Buy Add-On A for $Y/user.

This way, your users won't be confused about your pricing plan, and they can choose which premium feature they want, rather than subscribe and have all the premium features. Which also helps them save cost, and allow you as a developer to know which extensions are the more popular ones.

Then you can have 2 packages. Top up $X per user to upgrade from the Free Tier to Basic Tier, or $X per user (No more free 5 users) to upgrade from Free Tier to Premium Tier.

If you do this then you have to be clear on your copy how this works.

Something like Free 5 users FOREVER*!

*Only valid for teams on the Basic Tier.

You could do an interesting pricing in such a way that first 5 is free, above that, you pay $X for each ADDITIONAL seat instead of for 6, which makes no sense if there's no extra premium features.

If it is a team-based app, you can start thinking about things that your app can offer, but at a slower performance rate. Slack has it's 10,000 message cap. Dropbox has it's 5GB cap.

Depending on what you offer, I'm sure you can limit it somehow. Maybe free accounts can only have up to 5 users in a team? This is small enough that very very small agencies like startups can use your app while it's starting-up (hur hur), but once it's gained traction — and hopefully, grew a reliance on your app — they will subscribe to the premium version to raise it's user cap.

Or if you want to, you could also limit the amount of interaction. For e.g. if you're offering an invoicing app, limit the amount of invoice generated to 3 per month.

Without leaking your app's offerings, these are what I could think of.

I would suggest pricing it in such a way that the free version makes it very usable, but causes a small hassle, which will bug users to pay for premium.

e.g. Slack, perfectly usable in the free version. But if I want more than 5 integration with other apps, I got to upgrade. And my message history is capped at 10,000. Perfectly usable at the free tier. But the small things may annoy me to the point I want to upgrade if my company has funds to spare.

Marzan made a very good point with Dropbox and Invision. Both are perfectly usable products without paying, especially for individuals. But once you start to use them at a company / agency level, paying for it makes perfect sense.

I also use Zoho. You can even set up your own referral system to earn more email accounts by referring.

Same, except a different colored mushroom.

I'm interested to know this too. I purchased RIghtFont, but this seems like a good entry level app I can buy for friends.