Hire on Upwork

BestOS

Software for the next stack.

AI makes brochure sites cheap. Real products still need ownership — auth, data, bookings, mobile, and regulated systems. Remote across Europe, the UK, and the USA.

Start a projectHow we work
ReactNext.jsTypeScript.NET CoreVueReact NativeAngularRedisDockerPostgreSQLReactNext.jsTypeScript.NET CoreVueReact NativeAngularRedisDockerPostgreSQL
4+years shipping product
6countries served
AI-acceleratedbuild speed, senior review
NDA-readyhealthcare & pharma

Services

Clear offers. What’s included.

Every package lists deliverables, timeline, and revision rounds — so rewrites and edits stay predictable, not endless.

01from $280

Business site / landing (AI-assisted)

A clean offer page in a few days — AI drafts, senior polish, ready to publish.

3–7 days2 rounds of design/copy edits included; extra rounds from $40 each

Included

  • 1–5 page site (home + key sections) or a focused landing
  • Brand-aligned layout (your logo/colors or a clean default)
  • Headline + section copy rewrite/edit (EN or UA)
  • Mobile-responsive build + basic SEO (titles, meta, sitemap)
  • Contact / CTA wiring (form, phone, Upwork, or Calendly)
  • Deploy to your domain or a BestOS-hosted preview
  • Handoff: source access + short how-to for small text edits
02from $1,200

Custom web applications

React / Next.js apps with real auth, data, and workflows — not a disposable AI demo.

1–4 weeks by scope2 review cycles per milestone; change-requests re-quoted if out of scope

Included

  • Scoped feature set after discovery (written SOW)
  • UI for core flows (dashboard, forms, lists, settings)
  • Auth / roles when needed
  • API or database wiring for real data
  • Responsive desktop + mobile web
  • Staging demo + production deploy
  • Bug-fix window: 14 days after launch for defects in scope
03from $1,100

Booking & appointment systems

Services, staff, calendars, and client booking that businesses can run daily.

1–3 weeks2 UI/flow edit rounds on the booking UX; schedule rules changes counted as scope

Included

  • Service / staff / duration setup
  • Calendar & available time slots
  • Client booking form + confirmation state
  • Admin view to manage bookings
  • Email or webhook notify option (by stack)
  • Copy polish for booking screens
  • 14-day defect fix window after go-live
04from $750

Mobile app features

React Native features, fixes, and store-oriented releases for iOS and Android.

3–14 days by feature1–2 iteration passes on the feature; store rejection fixes for our build included once

Included

  • Feature or bugfix scoped in writing
  • UI implementation matching your design or production-grade polish
  • Device testing on key phones
  • Build for TestFlight / internal testing when applicable
  • Release notes for what changed
  • Handoff of PR / branch + short video or checklist
05from $900

.NET APIs & integrations

Production APIs, queues, cache, and third-party integrations — including regulated domains.

1–3 weeksContract/API shape locked after design review; additive endpoints re-quoted

Included

  • API design + implementation (.NET Core)
  • Auth, validation, and error handling
  • DB / Redis / queue pieces as needed
  • Third-party integration (payment, eHealth-style, CRM, etc.)
  • Basic tests on critical paths
  • Swagger / docs for your team
  • Staging deploy + smoke check
06from $1,800

MVP in 2–4 weeks

A shippable product slice with milestones. AI for scaffolding; architecture and QA stay human.

2–4 weeks1 polish pass after each milestone demo; big pivots = new estimate

Included

  • Discovery → written MVP scope (must-have only)
  • Clickable / usable core flows
  • Auth + primary data model
  • Weekly demo + shared board
  • Staging + production launch of the MVP slice
  • Copy pass on key screens
  • 14-day post-launch defect window + optional care plan
07from $600/mo

Monthly product care

Steady features, fixes, and releases without hiring a full-time engineer.

Rolling monthlyPriority queue agreed weekly; unused hours don’t roll unless stated in the plan

Included

  • Reserved senior hours (plan size agreed upfront)
  • Bug fixes + small features
  • Copy/UI tweaks and light rewrites
  • Dependency / security updates as needed
  • Short weekly sync or async update
  • Deployments included for work in the plan

Work

Selected systems

Live FitTracker screens, booking product UI, and NDA client delivery in healthcare / pharma — the work AI demos don’t replace.

FitTrackerMobile · Product

FitTracker

Founder product proof — live strength analytics with workout logging, training history, muscle recovery map, and analytics. Not a second agency brand; just shipped product evidence.

Founder product · App Store liveApp Storefittracker.store
Appointment booking constructorSaaS · Booking

Appointment booking constructor

Product UI for building services, staff schedules, time slots, and client bookings — aimed at clinics and service businesses.

SaaS · booking flows
Healthcare clinical frontendHealthcare · Frontend

Healthcare clinical frontend

Senior React work on clinical workflows, heavy forms, and reusable UI used daily by medical staff. Client product under NDA.

Client · NDA
Pharma & eHealth platformPharma · Full-stack

Pharma & eHealth platform

Full-stack .NET Core APIs, Vue/React modules, Redis, queues, and integrations (incl. eHealth-style domains) for pharmacy / medical operators.

Client · NDA
Cross-platform feature deliveryWeb · Mobile · Desktop

Cross-platform feature delivery

Web, mobile, and desktop feature work across React, Vue, Angular, React Native, and .NET for product teams that need velocity with senior ownership.

Multi-surface · retained work

Process

Start → build → finish

Same path for a $280 landing or a multi-week MVP. Clear gates so both sides know when work starts, when edits count, and when it’s done.

  1. Start
    01

    Intro call

    15–30 min: goals, users, deadline, budget band, and whether NDA is needed before details.

  2. Start
    02

    Papers & kickoff pack

    Sign NDA (if needed), then SOW / Upwork contract. You share brand assets, access, and examples of what “good” looks like.

  3. Start
    03

    Scope lock

    Written offer: deliverables, timeline, price, revisions, and what is out of scope. Work starts after deposit or Upwork milestone funding.

  4. Build
    04

    Build & demos

    Weekly (or milestone) demos. Feedback in one place. Included revision rounds are used here — not endless open edits.

  5. Finish
    05

    Acceptance

    You review against the SOW checklist. We fix in-scope defects. Out-of-scope ideas become a follow-up estimate.

  6. Finish
    06

    Handoff & close

    Deploy, credentials, source access, short handoff note. Final invoice / Upwork release. Optional monthly care starts if you want it.

Papers

Documents we use with clients

Keep it light but real. Upwork can wrap payment + contract; off-platform work uses the same checklist.

Before deep discovery

NDA (optional → recommended)

Mutual non-disclosure before you share product secrets, patient/business data, or unreleased designs. Standard for healthcare / pharma.

Before coding starts

SOW / Offer (always)

Statement of Work: what’s included, what’s not, timeline, price, revision rounds, and acceptance criteria. This is the source of truth.

With the SOW

Service agreement or Upwork contract (always)

Legal wrapper: parties, payment terms, IP ownership (client owns deliverables after full payment), liability limits, termination. On Upwork, the platform contract + milestones cover this.

Each payment

Invoice / milestones (always)

Deposit (often 30–50%) or funded Upwork milestones, then balance on acceptance. Monthly care = invoice at month start.

Kickoff week

Access & asset list (kickoff)

Domains, hosting, Git, stores, analytics, brand files, copy docs. Keeps the project from stalling on day 3.

At launch

Acceptance / handoff note (close)

Checklist signed off (email is enough), links to staging/prod, credentials shared securely, warranty window dates.

Studio

BestOS · Valentyn Riabinchak

Senior full-stack engineer building with React, Next.js, Vue, React Native, and .NET. AI for scaffolding speed; architecture, edge cases, and production quality stay human.

Ukraine · Poland · Czechia · Slovakia · United Kingdom · United States

View Upwork profile
FitTracker app screens — logging, history, body map, analytics

Contact

Start with a short call

Tell me the outcome you need. I’ll say what’s in scope, what papers we need, and a fixed next step.

Hire on Upworkhello@bestos.siteCall +380 99 288 0228

hello@bestos.site · +380 99 288 0228 · Remote · Mon–Fri 09:00–20:00 · Sat 10:00–16:00 (Europe/Kyiv)