Hello there!
Some time ago my friend and I were trying to set up bitcoin payments for our project.
We found it not very easy to do without fees and with minimal server requirements.
But finally I found the solution to that problem, and made it an opensource project.
Now it is targeting many audiences:

• Developers, having daemons for bitcoin and other coins, and SDK(https://sdk.bitcartcc.com) sharing same APIs for any coin, easy to create any kind of app
• Merchants, providing ready solutions for your stores to accept cryptocurrency payments with simpliest setup
• Server maintainers, providing simpliest setup which is basically copy pasting some commands and editing setting for yourself, with automatic updates(github -> docker hub -> end machines)
• Anyone else wanting to try out cryptocurrencies

It is aims to use minimal system resources and provide maximum efficiency.
In fact, all demos run on one server with 1 GB RAM and 25 GB disk, also hosting other projects. ( so ~= 250-500 MB RAM, depends on selected components + ~= 3 GB disk space for docker images and data).



How does that work?
Internally, at it's core, BitcartCC is just a wrapper around electrum wallet, providing consistent and stable interfaces.
So it doesn't download full blockchain, but still verifies needeed parts of it for your wallets via SPV(Simple Payment Verification).
That way it can run anywhere, including from some embedded device to powerful servers.
BitcartCC is self-hosted, and is without any third-party, so your keys-your bitcoin.
You can insert your x/y/z pub/prv or electrum seed in it and it'll just work.
When installing, you are free to install only things you need.
Are you developing your own app?
Then just install needed daemons.
Online shop?
Also pick powerful BitcartCC Merchants API, which will be enough for your shop in most cases.
Want to edit your products, add/remove discounts, configure email settings, downloadable content, watch invoices statuses? Add BitcartCC admin panel.
You have no store ready and want to start without even coding your own shop? Also add BitcartCC store template, and you're all set.
That way, more components may be added in future easily, and you can even add your own.
Diagram about how does that look when you have picked all available(for now) components:

We also support lightning network easily, your BitcartCC core acts as a lightning node.
Examples of stuff created with it:
For example, atomic swaps bot, supporting multiple currencies, fully opensource:
On telegram: @bitcart_atomic_tipbot
Source code:
https://github.com/MrNaif2018/bitcart-sdk/blob/master/examples/atomic_tipbot/bot.py
Full explanation how it works:
https://github.com/MrNaif2018/bitcart-sdk/blob/master/examples/atomic_tipbot/README.md
You can see more examples here:
https://github.com/MrNaif2018/bitcart-sdk/blob/master/examples

Note, this project is still in alpha stage, but with the power of our community it will get way better!
We are open to all your ideas, suggestions or contributions!
Links:
Github:
https://github.com/MrNaif2018/bitcart
https://github.com/MrNaif2018/bitcart-sdk
https://github.com/MrNaif2018/bitcart-admin
https://github.com/MrNaif2018/bitcart-frontend
https://github.com/MrNaif2018/bitcart-docker
https://github.com/MrNaif2018/bitcart-docs
Official site with key features listed:
https://bitcartcc.com
Docs:
https://docs.bitcartcc.com
SDK docs:
https://sdk.bitcartcc.com
Demos:
https://admin.bitcartcc.com (Admin panel)
https://store.bitcartcc.com (Store template)
https://demo.bitcartcc.com (API)
Communities:
Telegram: https://t.me/bitcartcc
Discord: https://discord.gg/8H2Sfdh
Twitter: https://twitter.com/BitcartCC

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Note: for those already seen similar thread, it is full reborn and rebranding of BitcartCC, old thread will be left for historical purposes.
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Thanks to ThomasV, and other creators of electrum wallet, without it it coudn't exist.
Thanks to fellow bitcoinians who helped us! We appreciate your comment and help.
Here are the people who helped us in our early learning process.

pooya87 https://bitcointalk.org/index.php?topic=4675338.msg42192404#msg42192404 , https://bitcointalk.org/index.php?topic=5062441.msg47536549#msg47536549
gentlemand https://bitcointalk.org/index.php?topic=4849637.msg43730558#msg43730558
LeGaulois https://bitcointalk.org/index.php?topic=4849637.msg43731727#msg43731727
shield132 https://bitcointalk.org/index.php?topic=4849637.msg43731960#msg43731960
OmegaStarScream https://bitcointalk.org/index.php?topic=5049531.msg46824331#msg46824331
hdtqisg https://bitcointalk.org/index.php?topic=5049531.msg46827739#msg46827739
Bergqvist https://bitcointalk.org/index.php?topic=5049531.msg46899183#msg46899183
AdolfinWolf https://bitcointalk.org/index.php?topic=5049833.msg46847968#msg46847968
mmo_online_1981 https://bitcointalk.org/index.php?topic=5049833.msg46951970#msg46951970
MadGamer https://bitcointalk.org/index.php?topic=5063890.msg47638168#msg47638168
mocacinno https://bitcointalk.org/index.php?topic=5063890.msg47638420#msg47638420
ETFbitcoin https://bitcointalk.org/index.php?topic=5065037.msg47672772#msg47672772
Zin-Zang https://bitcointalk.org/index.php?topic=5065037.msg47676670#msg47676670
HeRetiK https://bitcointalk.org/index.php?topic=5065037.msg47677068#msg47677068
bob123 https://bitcointalk.org/index.php?topic=5065037.msg47696157#msg47696157
Wind_FURY https://bitcointalk.org/index.php?topic=5065037.msg47725827#msg47725827
khaled0111 https://bitcointalk.org/index.php?topic=5092782.msg49032127#msg49032127
Heisenberg_Hunter https://bitcointalk.org/index.php?topic=5092782.msg49040673#msg49040673
BitMaxz https://bitcointalk.org/index.php?topic=5092782.msg49053041#msg49053041
Abdussamad https://bitcointalk.org/index.php?topic=5092782.msg49057412#msg49057412
Lucius https://bitcointalk.org/index.php?topic=5092782.msg49065938#msg49065938
hamburger https://bitcointalk.org/index.php?action=profile;u=20856 (in pm)

Thank you so much. We are hungry for ideas, suggestions and contributions. Please write to us here or telegram group.