Are there any general (not field-specific) researcher digital identification services or directories, similar to ORCID and ResearcherID?
Some of the obvious ones:
The ISNI initiative wants to assign unique identifiers to all "creators". (They take authors in the broad sense of individuals generating copyrightable content or something like that, since they include musicians and others.) That is about as "general" as you can want.
If you want to restrict to Academia, the arXiv author identifier is not specifically field-specific, though it is limited to fields which have an arXiv presence.
Since you didn't specify what is required of a "researcher digital identification service", social networks such as Academia.edu and ResearchGate which you mentioned in your other question can also serve the purpose of disambiguation of publishing records.
- Certain countries maintain their own databases of researchers residing there. The most comprehensive and successful seems to be that of Netherlands.
- The American Mathematical Society has recently starting maintaining author profiles as part of their MathSciNet service (I know that the question asked for "not field-specific"; I'll weasel and say that the AMS profiles include also those working in related sciences to mathematics, such as physicists and computer scientists, and some engineers.)
For a list of some of the other services, the International Repositories Infrastructure Wiki has a slightly out-dated list of such services. Note however some of the items listed there have stalled and shutdown since the last edit.
A few more creator/author/researcher identifiers:
- Scopus Author Identifier - automatically generated from author name and affiliation appearing in publications in the Scopus database
- Microsoft Research Academic Search for authors
- Google Scholar author profile aka. "My Citations"
Please note that ORCID lives within a reserved section of the International Standard Name Identifier (ISNI) namespace, see "ORCID and ISNI Issue Joint Statement on Interoperation", and works associated with an ORCID can be more than just publications but can include performances and presentations too, see "Supported Work Types" for a list.