Here is the full list of all 42 STEINS;GATE achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Unlocked all Achievements.
[Phone Trigger] Received all Gero Froggy wallpapers.
[Phone Trigger] Received all 13 RaiNet episode summaries.
Unlocked all CGs.
[Phone Trigger] Asked by Kurisu to buy cup noodles twice in a row.
Completed all endings.
Reached Steins Gate.
Reached Mayuri's ending.
[Phone Trigger] Received 3 wallpapers of characters from a chaotic head.
[Phone Trigger] Learned why Mayuri started making costumes.
Reached Luka's ending.
[Phone Trigger] Received 4 songs from a chaotic head.
[Phone Trigger] Offered tea by Faris.
Learned about Luka's relationship to his sister.
Reached Suzuha's ending.
Made 10 mistakes while attempting to set the PhoneWave (name subject to change)'s timer.
Reached Kurisu's ending.
Chapter 9 Clear
Unlocked 75% of CGs.
[Phone Trigger] Ignored a phone call.
Chapter 8 Clear
Chapter 7 Clear
Reached Faris's ending.
[Phone Trigger] Cleared someone's mail without reading it.
Chapter 6 Clear
Unlocked 50% of CGs.
Chapter 5 Clear
Chapter 4 Clear
Made friends with Kurisu via email.
[Phone Trigger] Received an unusual proposition from Suzuha.
Unlocked 25% of CGs.
Chapter 3 Clear
Chapter 2 Clear
Chapter 1 Clear
[Phone Trigger] Received 2 Upa wallpapers.
[Phone Trigger] Replied to an email.
[Phone Trigger] Changed ringtone.
[Phone Trigger] Viewed email send history at least once.
[Phone Trigger] Read an email.
[Phone Trigger] Changed phone wallpaper.
Prologue Clear
Started Steins;Gate.