www.dl2rum.de

It would add the ability for log search update from RUMlog.

http://www.clublog.org/tips.php

How to upload logs directly into Club Log from logging software (developer API)
As well as the main upload forms within the Club Log web site, there is another way to upload files directly which is designed to help developers wishing to add "Export to Club Log" features, or contesters and expeditioners who would like to have live logging updates to Club Log.
You can use HTTP POST to send ADIF files to http://www.clublog.org/putlogs.php. The POST form variables are as follows:
email: A registered email address in Club Log
password: The password to authenticate the email login
callsign: Optionally, the callsign into which the logs should be uploaded. If not set, the primary callsign of the account is used.
file: A multipart/form-data upload which is used to POST the ADIF file with the form
For an example form which also serves as a working test case, you may wish to load and view the source of this example page:
http://www.clublog.org/test_upload.html
When a file is passed to Club Log via this mechanism, it will be placed on the upload queue as normal. It is typically around 10 minutes later that the upload will then be processed, so remember to allow for this extra delay.

I'm not sure yet, for what ClubLog is useful. I have to register to find out more. I will put it on my list and will have a look on it later.

I was looking around, but I haven't find much information for developer. As far I understood you have to upload a full log. After that is should be useful to uploads QSOs again when the QSL status changes?
Which data must be uploaded?
Which data should be uploaded?
Which data can be uploaded?

It would add the ability for log search update from RUMlog.

What do you mean with "log search update" ?

This link talks about what ClubLog has to offer.
http://www.clublog.org/about.php

As far as developer information:

First, Login to ClubLog website, then enter/click link: http://www.clublog.org/tips.php About half way down, it talks about how to submit logs for developers. Logs can be updated by three different methods.
1) Login into site, and uploading an ADIF file.
2) Update by emailing ADIF to updates@clublog.org. It gets added to your log, and he checks for duplicates.
3) via POST method described on http://www.clublog.org/tips.php

As far as How often, you may do a full update only every month or quarter to catch up on confirmations. You can also upload the LoTW adi file, and record confirmations without resending your whole log. Secondly, you can do an incremental update of QSOs worked. This allows people to check your log to see if they are in your log.

For example, You can search my log for N8S or FO8RZ.
If you select http://www.clublog.org/logsearch/KB5HPL

FO8RZ expedition is in Club Log as well at http://www.clublog.org/charts/?c=FO8RZ#r

He also creates a Most Wanted DXCC list based on logs: http://www.clublog.org/mostwanted.php

It will do leaderboards for clubs. For example DARC, http://www.clublog.org/browse.php?club=29

Anyway, it was just an idea...

I haven't still found further information:

Which data must be uploaded?
Which data should be uploaded?
Which data can be uploaded?