user15492: I'm gathering a list of Bitcoin / Blockchain APIs. I mean web (REST) APIs that allow you to do basic blockchain queries through http(s) API calls, such as: getting the balance on an address, getting a list of transactions from or to an address, getting the details (inputs and outputs) for a transaction, et cetera.
I'm familiar with blocktrail.com, blockcypher.com, blockchain.info, and blockr.io, but I remember having seen others in the past. Any more?

user15358: https://developer.bitaps.com/
Block explorer API
Wallet API

user83611: Most complete list of blockchain explorers is present in the Bitcoin wiki:
https://en.bitcoin.it/wiki/Block_chain_browser
Note that some of these API providers are not maintained anymore. So be careful about selecting one. Also, only few explorers in the market support SegWit but it is used widely now so it should be taken into account.

user101498: There is now also the Esplora explorer / REST API. It's completely open source and you can host an instance yourself.
A public one runs at blockstream.info.
There is also the "mempool" open source explorer (which -as not indicated by the name- is a block explorer), even if its API is less complete than Esplora's one.
A public instance runs at mempool.space.

user44286: Checkout Bitquery GraphQL explorer APIs
Bitquery exposes single GraphQL endpoint to query data across multiple blockchains.
Currently, they support more than 20 blockchains and provide a unified API interface.
It's pretty easy to integrate with them and I am pretty sure this tech does not exist anywhere else.

user23123: Insight by bitpay:
https://insight.bitpay.com/
Block Explorer:
https://blockexplorer.com/
Bitcoin Chain:
https://bitcoinchain.com/block_explorer
There are many more in development, but these are ones I could find that you didn't list.

user90279: https://blockchair.com/api
API for BTC, BCH, LTC and ETH blockchains.

15492: <p>I'm gathering a list of <strong>Bitcoin / Blockchain APIs</strong>. I mean web (REST) APIs that allow you to do basic blockchain queries through http(s) API calls, such as: getting the balance on an address, getting a list of transactions from or to an address, getting the details (inputs and outputs) for a transaction, et cetera.</p>

<p>I'm familiar with blocktrail.com, blockcypher.com, blockchain.info, and blockr.io, but I remember having seen others in the past. Any more?</p>
 15358: <p><a href="https://developer.bitaps.com/" rel="nofollow noreferrer">https://developer.bitaps.com/</a>
Block explorer API
Wallet API</p>
 83611: <p>Most complete list of blockchain explorers is present in the Bitcoin wiki:
<a href="https://en.bitcoin.it/wiki/Block_chain_browser" rel="nofollow noreferrer">https://en.bitcoin.it/wiki/Block_chain_browser</a></p>
<p>Note that some of these API providers are not maintained anymore. So be careful about selecting one. Also, only few explorers in the market support SegWit but it is used widely now so it should be taken into account.</p>
 101498: <p>There is now also the <a href="https://github.com/Blockstream/esplora" rel="nofollow noreferrer">Esplora</a> explorer / REST API. It's completely open source and you can host an instance yourself.</p>
<p>A public one runs at <a href="https://blockstream.info/" rel="nofollow noreferrer">blockstream.info</a>.</p>
<p>There is also the <a href="https://github.com/mempool/mempool" rel="nofollow noreferrer">&quot;mempool&quot; open source explorer</a> (which -as not indicated by the name- is a block explorer), even if its API is less complete than Esplora's one.</p>
<p>A public instance runs at <a href="https://mempool.space/" rel="nofollow noreferrer">mempool.space</a>.</p>
 44286: <p>Checkout <a href="https://explorer.bitquery.io/graphql" rel="nofollow noreferrer">Bitquery GraphQL explorer APIs</a></p>
<p><a href="https://bitquery.io/" rel="nofollow noreferrer">Bitquery</a> exposes single GraphQL endpoint to query data across multiple blockchains.</p>
<p>Currently, they support more than 20 blockchains and provide a unified API interface.</p>
<p>It's pretty easy to integrate with them and I am pretty sure this tech does not exist anywhere else.</p>
 23123: <p>Insight by bitpay:</p>

<p><a href="https://insight.bitpay.com/" rel="nofollow">https://insight.bitpay.com/</a></p>

<p>Block Explorer:</p>

<p><a href="https://blockexplorer.com/" rel="nofollow">https://blockexplorer.com/</a></p>

<p>Bitcoin Chain:</p>

<p><a href="https://bitcoinchain.com/block_explorer" rel="nofollow">https://bitcoinchain.com/block_explorer</a></p>

<p>There are many more in development, but these are ones I could find that you didn't list.</p>
 90279: <p><a href="https://blockchair.com/api" rel="noreferrer">https://blockchair.com/api</a></p>

<p>API for BTC, BCH, LTC and ETH blockchains.</p>
