Air Explorer support the next clouds:

Dropbox
2 GB of free storage
Sign up: Dropbox

Mega
50 GB of free storage
Sign up: mega.nz

Google Drive
15 GB of free storage
Sign up: drive.google.com

Onedrive
5 GB of free storage
Sign up: onedrive.live.com

Onedrive for Business
No free storage
Sign up: onedrive.live.com

Onedrive for China

Box
10 GB of free storage
Sign up: box.com

Yandex
10 GB of free storage
Sign up: disk.yandex.com

Naver
30 GB of free storage
Sign up: cloud.naver.com

FTP

SFTP

WebDav
You can add and use any WebDAV server such as:
-cloudme.com,
-powerfolder.com,
-opendrive.com,
-owndrive.com,...

Mail.ru
25 GB of free storage
Sign up: cloud.mail.ru

Baidu
2 TB of free storage
Sign up: yun.baidu.com

Magenta
10 GB of free storage
Sign up: telekom.de/magentacloud

Hidrive
5 GB of free storage
Sign up: hidrive.com

pCloud
20 GB of free storage
Sign up: pcloud.com

Datto Drive
2 GB of free storage
Sign up: datto.com

Stack Storage
Sign up: transip.be/stack/

Mail.com
2 GB of free storage
Sign up: mail.com

4shared
16 GB of free storage
Sign up: 4shared.com

SharePoint Online
Sign up: office.com/sharepoint

SharePoint China
Sign up: office.com/sharepoint

AWS S3
Sign up: aws.amazon.com/es/s3/

Koofr
2GB of free storage
Sign up: koofr.eu

Backblaze
Sign up: backblaze.com/b2

Teracloud
10GB of free storage Sign up: teracloud.jp

Owncloud
Sign up: ownlcoud.com

Nextcloud
Sign up: nextcloud.com

Mediafire
10 GB of free storage
Sign up: mediafire.com

ADrive
Sign up: adrive.com

Jottacloud
5 GB of free storage
Sign up: jottacloud.com

Huawei
5 GB of free storage
Sign up: huawei.com

Orange Flexible Engine
Sign up: orange-business.com

Onlime.dk
5 GB of free storage
Sign up: onlime.dk

Nutstore
Sign up: jianguoyun.com