OpenCart is a popular open-source storefront. It is similar to other e-commerce web interfaces such as Shoppify and WooCommerce. It features integration with several fiat payment networks. This page lists some plugins that integrate with bitcoin payment methods.
Sites using the Open Source OpenCart e-commerce system, available in many web hosting packages, can configure their stores to use third party payment processing companies. This enables companies using OpenCart to accept bitcoin from their customers with minimal effort or risk.
BitcoinPay.com is a European  Bitcoin Payments processor. It has a OpenCart Bitcoin Payments Plugin which registered users can integrate into their e-commerce stores, to enable them to take payments within the Eurozone, as well as local payments in Czech Koruna, and Polish Zloty. Settlements can be set to remit in any percentage of fiat and bitcoin.
Apirone Payment Gateway
Apirone has a plugin for OpenCart 3.x and 2.3+ which lets users accept Bitcoins on their online stores with a fixed commission, regardless of the amount order. No registration is or KYC/AML procedure is needed. It supports Segwit addresses and use of the TOR network. (Extension link)
Blockonomics has an opencart module that allow merchants to receive bitcoin directly to wallet. All major HD Wallets like blockchain.info, electrum, trezor are supported. The plugin is open source and can be access on github
NOWPayments provides merchants with an OpenCart payment gateway, which lets them accept Bitcoin payments in their online store.  To receive online payments, one needs to sign up for NOWPayments account, configure the store settings: specify wallet address and generate API Key, and install OpenCart plugin. The solution is free of charge.
Old OpenCart Bitcoin Extension
An older extension made by John Atkinson (jga) of  - the original source of this page - is no longer actively maintained as of mid 2013. Information relating to it is below to maintain the record.
An OpenCart payment module that communicates with a bitcoin client using JSON RPC.
This code accurately converts USD to BTC using the up-to-the-minute MtGox average. It is completely self contained and requires no cron jobs or external hardware other than a properly configured bitcoind server. Every order creates a new bitcoin address for payment and gives it a label corresponding to the order_id of the order. It installs like any other OpenCart plugin and it is completely integrated with OpenCart. It was first made available on September 21, 2012.
Below is a non-exhaustive list of bitcoin payment gateway extensions for OpenCart.
- OpenCart 3.x Bitcoin extension OpenCart 3.x Bitcoin extension, opensource on GitHub
- OcStore and OpenCart 2.3 Bitcoin extension OcStore and OpenCart 2.3 Bitcoin extension, opensource on GitHub
- OpenCart Bitcoin project on GitHub
- Opencart_v2 Bitcoin project on GitHub
- OpenCart Online Shops Welcome Bitcoin Payments
- Accept Bitcoins with OpenCart plugin
- BTC Gear
- 50 BTC BOUNTY: BITCOIN OPEN CART PAYMENT MODULE!