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Cap'n Proto Alternatives
Similar projects and alternatives to Cap'n Proto
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InfluxDB
InfluxDB – Built for High-Performance Time Series Workloads. InfluxDB 3 OSS is now GA. Transform, enrich, and act on time series data directly in the database. Automate critical tasks and eliminate the need to move data externally. Download now.
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zig
General-purpose programming language and toolchain for maintaining robust, optimal, and reusable software.
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carbon-lang
Carbon Language's main repository: documents, design, implementation, and related tools. (NOTE: Carbon Language is experimental; see README)
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SaaSHub
SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
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Apache Arrow
Apache Arrow is the universal columnar format and multi-language toolbox for fast data interchange and in-memory analytics
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simdjson
Parsing gigabytes of JSON per second : used by Facebook/Meta Velox, the Node.js runtime, ClickHouse, WatermelonDB, Apache Doris, Milvus, StarRocks
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Sandstorm
Sandstorm is a self-hostable web productivity suite. It's implemented as a security-hardened web app package manager.
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ustore
Multi-Modal Database replacing MongoDB, Neo4J, and Elastic with 1 faster ACID solution, with NetworkX and Pandas interfaces, and bindings for C 99, C++ 17, Python 3, Java, GoLang 🗄️
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SaaSHub
SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a better Cap'n Proto alternative or higher similarity.
Cap'n Proto discussion
Cap'n Proto reviews and mentions
Posts with mentions or reviews of Cap'n Proto.
We have used some of these posts to build our list of alternatives
and similar projects. The last one was on 2025-06-01.
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Writing your own C++ standard library part 2
Have you seen libkj [1]? I've used it and really enjoy working with it. It has a rust-like owned pointer and the whole library uses these smart pointers.
It has proper container classes based on B-trees and its also got an async runtime.
[1] https://github.com/capnproto/capnproto/blob/v2/kjdoc/index.m...
- The first year of free-threaded Python – Labs
- Ask HN: Which Opens Source Software have the sexiest code?
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Begrudgingly Choosing CBOR over MessagePack
Just curious if you considered Cap'n Proto as another option, or if it wasn't in the running?
[1] https://capnproto.org/
- Cap'n Proto: High-Performance Serialization and RPC for Modern C++
- The Simdjson Library
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Demystifying the Protobuf Wire Format
To be fair, if that's what you need ProtoBuf isn't the only option. Cap'n Proto[1], JSON Schema[2], or any other well supported message-definition language could probably achieve that as well, each with their own positives and negatives.
[1]: https://capnproto.org/
[2]: https://json-schema.org/
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Mysterious Moving Pointers
Yeah I pretty much only use my own alternate container implementations (from KJ[0]), which avoid these footguns, but the result is everyone complains our project is written in Kenton-Language rather than C++ and there's no Stack Overflow for it and we can't hire engineers who know how to write it... oops.
[0] https://github.com/capnproto/capnproto/blob/v2/kjdoc/tour.md
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Show HN: Comprehensive inter-process communication (IPC) toolkit in modern C++
- may massively reduce the latency involved.
Those sharing Cap'n Proto-encoded data may have particular interest. Cap'n Proto (https://capnproto.org) is fantastic at its core task - in-place serialization with zero-copy - and we wanted to make the IPC (inter-process communication) involving capnp-serialized messages be zero-copy, end-to-end.
That said, we paid equal attention to other varieties of payload; it's not limited to capnp-encoded messages. For example there is painless (<-- I hope!) zero-copy transmission of arbitrary combinations of STL-compliant native C++ data structures.
To help determine whether Flow-IPC is relevant to you we wrote an intro blog post. It works through an example, summarizes the available features, and has some performance results. https://www.linode.com/blog/open-source/flow-ipc-introductio...
Of course there's nothing wrong with going straight to the GitHub link and getting into the README and docs.
Currently Flow-IPC is for Linux. (macOS/ARM64 and Windows support could follow soon, depending on demand/contributions.)
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Condvars and atomics do not mix
FWIW, my C++ toolkit library, KJ, does the same thing.[0]
But presumably you could still write a condition predicate which looks at things which aren't actually part of the mutex-wrapped structure? Or does is the Rust type system able to enforce that the callback can only consider the mutex-wrapped value and values that are constant over the lifetime of the wait? (You need the latter e.g. if you are waiting for the mutex-wrapped value to compare equal to some local variable...)
[0] https://github.com/capnproto/capnproto/blob/e6ad6f919aeb381b...
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A note from our sponsor - InfluxDB
www.influxdata.com | 24 Jun 2025
Stats
Basic Cap'n Proto repo stats
73
12,240
9.1
6 days ago
capnproto/capnproto is an open source project licensed under GNU General Public License v3.0 or later which is an OSI approved license.
The primary programming language of Cap'n Proto is C++.
Sponsored
InfluxDB – Built for High-Performance Time Series Workloads
InfluxDB 3 OSS is now GA. Transform, enrich, and act on time series data directly in the database. Automate critical tasks and eliminate the need to move data externally. Download now.
www.influxdata.com