MarkLogic vs Riak: What are the differences?
Developers describe MarkLogic as "Schema-agnostic Enterprise NoSQL database technology, coupled w/ powerful search & flexible application services". MarkLogic is the only Enterprise NoSQL database, bringing all the features you need into one unified system: a document-centric, schema-agnostic, structure-aware, clustered, transactional, secure, database server with built-in search and a full suite of application services. On the other hand, Riak is detailed as "A distributed, decentralized data storage system". Riak is a distributed database designed to deliver maximum data availability by distributing data across multiple servers. As long as your client can reach one Riak server, it should be able to write data. In most failure scenarios, the data you want to read should be available, although it may not be the most up-to-date version of that data.
MarkLogic and Riak can be categorized as "Databases" tools.
"RDF Triples" is the primary reason why developers consider MarkLogic over the competitors, whereas "High Performance " was stated as the key factor in picking Riak.
Riak is an open source tool with 3.24K GitHub stars and 530 GitHub forks. Here's a link to Riak's open source repository on GitHub.