The most notable text database system that has many text management features integrated together is Lotus Notes. It operates as a peer-to-peer networked text database management system.
Most features are able to operate both on "servers" (e.g. On hosts that act as central data repositories) and on "clients" (e.g. On hosts that are used by "end-users.") It doesn't have quite the sophistication of the high-end "document management systems" (in particular, it doesn't offer much in terms of archival policies and document versioning), but it's much easier to configure than most other "document management systems."
Lotus Notes features such things as:
Distributed data management and replication.
It is easy, for instance, to "replicate" a database from one of the central servers to one's personal laptop PC so that the data is both accessible and changeable while you're disconnected from the network, and hence disconnected from the server. Upon reconnection to the central server, you can both submit changes that you prepared offline and receive changes that were made in your absence. A crucial point is that this provides the functionality automatically, which is exceedingly important if unsophisticated users are to make use of the replication system. This is really valuable for those easily-stolen laptop computers, as it means that it's easy to back up the database.
The replication architecture seems to most resemble that of a news server, with a rather less vigorous expiry policy. (Since the document "groups" are smaller, the USENET "expire-before-reading" policy has little value.) A small NNTP server such as Leafnode might be a reasonable way to replicate the replication functionality on a small system. This also implies the use of news-like functionality for storage and retrieval of data.
Incidentally, the notion that Notes can be treated basically as a news server is nicely supported by the fact that if you export data as "Structured text," it comes out as a set of tagged lines remarkably similar in format to news header lines.
Full text search option
Not unlike Glimpse, although with a somewhat nicer built-in, universally-available, interface.
A Form-based user interface
Multiple database views
Rather similar to sorting/selecting on the basis of various header lines, this also allows users to add "folders" to data hierarchies. In the news context, this means that users can create things that rather resemble subgroups.
Integrated mail system
This has the interesting implication that mail is treated identically to news. My incoming mail gets put into my Inbox folder, and I can then redistribute it to other folders as necessary.
Data security via encryption, digital signatures, and ACLs
Notes uses RSA and related digital signature technology to authenticate users.
It also uses access control lists to determine what tasks users can perform within a database.
Databases can be stored in encrypted form with a variety of encryption "grades," which is of particular value for ensuring security on easily-stolen laptops. Organizations that use laptops extensively should consider adopting Lotus Notes for this reason alone.
Integrated/embedded scripting language
LotusScript is rather like an "Object-Oriented-BASIC" language that allows control of lots of stuff on the system. This includes things like:
Programming "agents" that forward documents to different folders, perhaps along with other filtering (ala procmail). (Used for forwarding documents, archiving, purging, generally filtering documents.)
Controlling the agents
Validating values in forms
Timed execution of code on a host
Controlling import/export of data to/from external systems
Managing "work tasks"
Extracting data from one database into another, for instance:
Turning email into an appointment in the appointment database
Ditto for tasks in a "task/work/to-do" database
It's not apparent from the export format precisely how this is done, but documents are allowed to contain within their bodies references or "links" to other documents, possibly in other databases, potentially on remote servers. These "links" can also represent inclusions of files (e.g. a spreadsheet document), and most recently, Web URLs.
Linking seems to be managed on the client side. Interestingly, the new "Web-enabled" version of Notes manages things via conversions of HTML into Notes data structures, and vice-versa, as appropriate for the client, and does so on the appropriate "server." If you connect to a web site using a Notes client, a subprocess on the client takes the HTML that was transmitted and converts it into a Notes screen/form. Conversely, when a web browser connects to a Notes server, the Notes server takes the screen/form, and converts it into HTML "on the fly." Apparently there must be a reasonable isomorphism between Notes forms and HTML forms.
Notes provides a useful and fairly rich set of functionality, and often represents a much better data repository than a "dumb" LAN file system. Granted that it is probably less storage-efficient, a cost paid for value gained in speed and robustness.
It is missing the ability to reflect structures internal to documents as can be provided by SGML .