Some free time side projects:

gosnarkstudy:
Go
zkSNARK implementation from scratch (compiler, setup, prover, verifier) 
gobellmanverifier:
Go
Groth16 zkSNARK bellman proof verifier using cloudflare/bn256 Pairing 
babyjubjubrs: BabyJubJub elliptic curve implementation in
Rust

poseidonrs: Poseidon hash implementation in
Rust

goblindsecp256k1: Blind signatures over secp256k1 in
Go
(With the compatible Typescript implementation) 
ringsignaturesrs: bLSAG ring signatures implementation in
Rust

ipars: modified Inner Product Argument (IPA) version from Halo paper in
Rust
using arkworks. 
kzgcommitments: KateZaveruchaGoldberg (KZG10) Polynomial Commitments in
Go

godht: Kademlia DHT implementation in
Go

merkletreers: Sparse MerkleTree implementation in
Rust

gomerkletree: Sparse MerkleTree implementation in
Go

shamirsecretsharing: Shamir's Secret Sharing
Rust
&Go
implementation +WASM
lib  kvartalo: a local social cryptocurrency for neigbourhoods, that we are using in a Barcelona neighbourhood as experiment. Build on top of Ethereum blockchain & Tendermint Core

gochip8: CHIP8 virtual machine emulator written in
Go

chip8rs: CHIP8 virtual machine emulator written in
Rust

fftrs: Fast Fourier Transform (FFT) implementation in
Rust
 miksi: Ethereum zkcoinmixer where all the computation & constructions are done offchain and then proved inside a zkSNARK to the smartcontract. (live demo on testnet)
Recent Work:
Vocdoni & Aragon (current) 
Decentralized governance & voting tooling.Design and implementation of anonymous voting solutions using zkSNARKs. Introduced some design optimizations in the circuits which reduced the number of constraints.
Also, contributed to vocdoni/vocdoninode adding zk related code.
Other stuff implemented:
 vocdoni/keccak256circom: ethereum sha3 (keccak256) hash function implemented in a Circom circuit
 vocdoni/zkcensusproof: anonymous census proof circuit used in Vocdoni's Blockchain
 vocdoni/arbo: optimized MerkleTree which parallelizes by CPUs for faster computation, compatible with circomlib implementation
 OVOTE technical document
 Forum post with a high level explanation.
 aragonzkresearch/ovote: implementation of the OVOTE circuits, smart contracts & libs
 aragonzkresearch/ovotenode: OVOTE backend node implemented in Go
Hermez zkRollup 
Decentralized zkRollup on Ethereum.Main task has been to implement the Hermez node, used to launch the mainnet of the zkRollup network:
hermeznetwork/hermeznode
My focus has been mainly in the TxSelector, TxProcessor (managing the rollup state tree) and BatchBuilder (generating the data structure compatible with the zkSNARK circuits to do the proof generation).
iden3 
Scalable decentralized identity system with privacy by design by using zero knowledge proofs.Design and specify the core protocol, develop the core libraries, servers, smart contracts, zk circom circuits and zkSNARK Groth16 Go prover.
 iden3/goiden3crypto: cryptographic primitives (SNARKfriendly) used in iden3
 iden3/goiden3core: core implementation of the iden3 system
 iden3/gocircomproververifier: implementation of the Groth16 zkSNARK Prover and Verifier compatible with Circom
 iden3/circuits: zkSNARK circuits used by the iden3 core protocol