1. Does the DriveHQ service allow the several users to be logged-on at the same timeand work on the same document at the same time; (or for the same user to be logged-on from different pcs at same time and work on the same doc. at the same time) ?
Yes, it supports. Please be careful that if two different people are working on the same file at the same time, they will overwrite changes made by each other. For more info on how to work this out, please read more at the bottom of this message.
2. Does DriveHQ support file versioning ?
If you use DriveHQ Online Backup, it supports backing up multiple versions of files. The regular web-based storage or DriveHQ FileManager doesn't support file versioning.
3. If so, does DriveHQ offer these features in the free service as well?
You can test almost all features with the free service, though it (free service) does have restrictions, so it may not be suitable for business use.
Thanks in advance.
Regarding multiple user accessing the same file, can DriveHQ lock a file?
Please note it is very hard to lock a file over the Internet using HTTP. A user can open a file using a web browser; he can then walk away, or shut down his computer or his browser crashes and he starts a new web browser. It is not possible for the web server to tell if the user will use the file again. If the server locks the file, then it could cause nobody else can access the file even if the user is no longer using it.
To support locking, it is recommended to set a rule among your team, e.g. when multiple people are working on one file "Project.doc", then before User A starts modifying it, he should change the file name to "Project_UserA_DATE.doc", after he finished, he can rename it to "Project.doc". If everybody does the same, you won't have two users working on the same file at the same time.