Products

Subscription apps by Purple Hardstone LLC

Alongside our engineering work, we build and operate our own subscription apps for web, iPhone and Android. Every product is a digital service — no physical goods are shipped.

StudyWithKeldra

An AI-assisted study and exam-preparation app for web, iPhone and Android: flashcards built from your own notes, spaced-repetition review, quizzes, mock exams and exam-readiness tracking for students and certification candidates.

Plans and pricing (USD)

  • Study — $14.99/month or $89.99/year
  • Exam Prep — $24.99/month or $119.99/year

Every new account gets a 7-day free trial with everything unlocked. Subscriptions renew automatically each month or year until cancelled.

Visit StudyWithKeldraTermsPrivacyRefund policy

Product support: support@studywithkeldra.com

SkyLingoSift

An AI-powered language-learning app for web, iPhone and Android: real spoken conversation practice with honest pronunciation scoring, grammar corrections explained in plain language, and vocabulary flashcards built automatically from your own conversations — in English, Spanish, French, German, Japanese and Portuguese.

Plans and pricing (USD)

  • Premium — $9.99/month or $69.99/year

Every new account gets a 7-day free trial with everything unlocked. Monthly and Annual renew automatically until cancelled.

Visit SkyLingoSiftTermsPrivacyRefund policy

Product support: support@skylingosift.com

NexaVella

A business-management platform for beauty professionals — hairstyling, barbering, nail care, skin care, massage & spa and cosmetology: online booking and appointments, customers, staff, services and products, invoicing, SMS and email notifications, and an AI Business Assistant that answers customer questions from your own FAQs. Works on web, iPhone and Android.

Plans and pricing (USD)

  • Starter — $49.99/month
  • Professional — $89.99/month
  • Enterprise — $179.99/month

Every new account gets a 7-day free trial. Plans renew automatically each month until cancelled.

Visit NexaVellaTermsPrivacyRefund policy

Product support: support@nexavella.com

More subscription apps are in development under the same company.

How billing works

  • In our iPhone and Android apps, subscriptions are bought and managed through the Apple App Store or Google Play, which also handle those refunds.
  • On the web, you subscribe directly from us and pay securely by debit or credit card. Refunds for web purchases follow each product's refund policy.
  • You can cancel at any time and keep access until the end of the period you paid for.