In random order:

123contactform.com
I no longer create forms myself for my website, but I just borrow a form from this site. It’s super easy to make forms, and to use them elsewhere (like here a form I used to find co-workers on a project).

Unicode code converter
whenever I run into problems with Unicode, and I need to convert characters, this is where I find the knowledge and the tools to solve the problem.

UTF-8 Encoding Debugging Chart
if a document contains a glyph shift, I search for “actual” and replace by the “expected” character.

Mailchimp.com
for sending out mass mailings. I’m paying a license fee now, but I used this tool for free for many years.

TMX Translation memory creator
sometimes you need to create a TMX quickly; not a super high tech service, but it often gets the job done in a blink of an eye.

Trello.com
to create lists with cards; I use this to keep my customer up to date on the status of a project, and I let them create cards as well (for instance for issues they encounter)

Smallpdf.com
I no longer use an expensive suite to manipulate PDF files, but this one.

RegEx101.com
It’s always easier to write regex with some help, examples… (RegexBuddy is still better, but this one is online).

LT-innovate.org/lt-observe/resources-list
Whenever I need to look for training data, this is my fist stop.

Cloudconvert.com
To convert file formats. I still must get the first file that I cannot convert. (Databases are the only blind spot I found so far.)

Moqups.com
I ask my customers to draw the application they have in mind. It is always easier to talk about something when we have the same image in our head.

Transferwise.com
Last time I used my own bank to pay a colleague in a foreign currency, must have been years ago. TransferWise is cheap, fast and reliable.

virustotal.com
My customers sometimes send me files I don’t want to open just like this. I have an good anti-virus scanner on my laptop, but still, in case of doubt, I use an online scanner first. Better safe then sorry.

guerrillamail.com
I don’t always need to/want to use my own mail address. Here I can generate a temporary mail address.

meetfranz
Not really an online tool, but a tool to centralize all communication (Messenger, Whatsapp, Skype, Hangouts, Gmail…)

Do you use online tools that you can’t do without anymore? Please share them with us.