What is NapSac?
NapSac is a free puzzle and thinking game for iOS, Android and the web, based on the knapsack problem from computer science. Players choose items with a value and a weight to maximize total value without exceeding the backpack's capacity.
Is NapSac free?
Yes. NapSac is free to download and play on iOS and Android, with no ads and no real-money purchases.
Who is NapSac for?
NapSac is suitable for players age 8 and up who enjoy logic puzzles, brain training, daily competitions, or competitive multiplayer.
What game modes does NapSac have?
Adventure (60+ puzzles across themed arenas), Daily Challenge (one shared puzzle per day with global leaderboard), Weekly Arena (a new themed arena each week), Time Attack (endless against the clock), ranked Battles (PvP), and asynchronous Friend Challenges.
Pack light. Think heavy.
Your backpack is hungry for treasures. Pack the most valuable items without overloading it. Solve puzzles, conquer arenas, battle friends and compete with players worldwide.
How It Works
Simple to learn, endlessly challenging. Based on the famous knapsack problem from computer science.
Meet the Items
Each item has a value and a weight.
Tap to Select
Tap items to add them to your backpack. Watch the capacity bar fill up.
Watch Your Weight
Find the best combination... but don't exceed your backpack's capacity.
Earn Stars
Find the best value to earn stars.
Try It Right Now
This is a real puzzle. Select items to find the best value without exceeding the weight limit. Can you find the perfect solution?
Six Ways to Play
Whether you want a chill solo adventure, a daily ranked race, or a real-time duel with a friend, there is a mode for you.
Adventure
CampaignExplore themed arenas across 320 puzzles. From Grasslands to Summit, each arena gets harder. Defeat bosses to unlock the next world.
Daily Challenge
DailyOne puzzle per day, same for everyone worldwide. Race against the clock, climb the global leaderboard, and keep your streak alive.
Weekly Arena
WeeklyA new themed arena every week. Solve them all to capture Naps.
Time Attack
EndlessHow many puzzles can you solve before time runs out? A fast-paced endless mode that tests your speed and accuracy.
Battles & Challenges
VersusDuel friends and rivals on the same puzzle. Send asynchronous challenges or climb the ranked PvP ladder from Rookie to Grandmaster.
My NapSac
CollectionSpend your hard-earned stars to collect adorable Nap companions, decorate your world with ponds and trees, and watch your village grow.
Why You'll Love It
NapSac blends brain-teasing puzzles with a playful adventure that keeps you coming back day after day.
Train Your Brain
Based on the NP-complete knapsack problem. Every puzzle is a unique optimization challenge.
Global Competition
Same daily puzzle for everyone. Compete for the top spot on the worldwide leaderboard.
Battle Friends
Send challenges to friends, accept their duels, and climb a ranked PvP ladder.
Daily Streaks
Solve challenges to build your streak. Reminders are optional and fully under your control.
Themed Arenas
Journey through Grasslands, Forge, Inferno, Crystal Caves, Summit and rotating weekly arenas.
Earn Stars & Medals
3 stars for first-try perfection, gold medals for monthly podiums. Collect them all to unlock new content.
Play Anywhere
Optional account to sync progress across devices. Play offline anytime — your scores sync when you reconnect.
11 Languages
English, French, German, Spanish, Italian, Portuguese, Dutch, Japanese, Korean, Chinese and Russian.
Meet the Characters
Your backpack has many moods. Collect them all in My NapSac.
Ready to Pack?
Download NapSac for free and start your puzzle adventure today. Prove you're smarter than a backpack.