From the OpenCitations Blog:
The four projects are similar, in that they each are independently using text mining and optical character recognition or PDF extraction techniques to extract citation information from the reference lists of published works, and are making these citations available as Linked Open Data. Three of the four will also use the OpenCitations Corpus as publication platform for their citation data. The academic disciplines from which these citation data are being extracted are social science, humanities and economics.
The four projects profiled in the blog post are:
1. Linked Open Citation Database (LOC-DB)
2. The EXCITE (Extraction of Citations from PDF Documents) Project
3. The Venice Scholar Index
4. CitEcCyr – Citations in Economics published in Cyrillic